Deuterated compounds

ABSTRACT

Described herein are compounds of formula (I) as defined herein, which comprise a greater proportion of deuterium to protium than naturally found in hydrogen; and compositions, including pharmaceutical compositions, comprising these compounds and optionally analogous compounds of formula (I), which are not deuterium-enriched. These compounds and compositions are of use in therapy, in particular in the treatment of psychiatric or neurological disorders. Varying the amounts of the different compounds within the compositions of the invention allows tailoring of the compositions&#39; therapeutic effects. A particularly efficient synthetic method which enables compounds of formula (I) and related compounds of formula (I′) is also provided.

BACKGROUND

Classical psychedelics have shown preclinical and clinical promise intreating psychiatric disorders (Carhart-Harris and Goodwin,Neuropsychopharmacology 42, 2105-2113 (2017)). In particular, psilocybinhas demonstrated significant improvement in a range of depression andanxiety rating scales in randomised double blind studies (Griffiths etal. Journal of Psychopharmacology, 30(12), 1181-1197 (2016)). Efficacyof psilocybin has been shown in depression (R. L. Carhart-Harris et al.,Psychopharmacology, 2018, 235, 399-408), end of life anxiety (R. R.Griffiths et al., J. Psychopharmacol., 2016, 30, 12, 1181-1197) andaddiction (M. W. Johnson, A. Garcia-Romeu and R. R. Griffiths, Am. J.Drug Alcohol Abuse, 2017, 43, 1, 55-60), and is currently beinginvestigated for several other mental health disorders that are rootedin psychologically destructive patterns of thought processing (AnorexiaNervosa: NCT #NCT04052568).

5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is an endogenous tryptaminefound in human blood, urine, and spinal fluid (S. A. Barker, E. H.McIlhenny and R. Strassman, Drug Test. Anal., 2012, 4, 7-8, 617-635; F.Benington, R. D. Morin and L. C. Clark, J. Med. Sci., 1965, 2, 397-403;F. Franzen, and H. Gross, Nature, 206, 1052; R. B. Guchhait, J.Neurochem., 1976, 26, 1, 187-190), and has been shown to exhibitprotective and therapeutically relevant effects. Antidepressantproperties have been shown in rodents administered 5-MeO-DMT (M. S. Rigaet al., Neuropharmacology, 2017, 113, A, 148-155). In addition, a highnumber of users of 5-MeO-DMT, having administered it in different forms,reported therapeutic effects attributed to its use, including improvedpost-traumatic stress disorder, depression and anxiety (A. K. Davis etal., J. Psychopharmacol., 2018, 32, 7, 779-792). 5-MeO-DMT has alsoexhibited the potential to treat substance abuse disorders (V. Dakic etal., Sci. Rep., 2017, 7, 12863).

N,N-dimethyltryptamine (DMT) is also understood to hold therapeuticvalue as a short-acting psychedelic. A review of research into thebiosynthesis and metabolism of DMT in the brain and peripheral tissues,methods and results for DMT detection in body fluids and the brain, newsites of action for DMT, and new data regarding the possiblephysiological and therapeutic roles of DMT is provided by S. A. Barkerin Front. Neurosci., 12, 536, 1-17 (2018). In this review, DMT isdescribed as having a possible therapeutic role in the treatment ofdepression, obsessive-compulsive disorder, and substance abusedisorders.

N-Methyltryptamine (NMT) is often extracted together with DMT and5-MeO-DMT from the bark, shoots and leaves of several plant genera. NMTis reported to have psychedelic properties: smoking NMT gives “visuals”at 50-100 mg, with a duration of 15-30 seconds (Shulgin, A. and Shulgin,A., 2002, THIKAL: the continuation, Transform Press).

The duration of action of DMT (under 20 minutes) is so short as to limiteffective therapy. Whilst administration protocols have been developedto extend the immersive psychedelic experience of DMT (Gallimore andStrassman (2016), A model for the application of target-controlledintravenous infusion for a prolonged immersive DMT psychedelicexperience, Frontiers in Pharmacology, 7:211), these protocols may carryrisk of toxic build-up in patients who are poor metabolisers of DMT (forfurther discussion see Strassman et al (1994), Dose response study ofN,N-dimethyltryptamine in humans, Arch Gen Psychiatry 51, 85).

DMT and its substituted analogues, such as 5-MeO-DMT, are understood tobe primarily inactivated through a deamination pathway mediated bymonoamine oxidases (MAOs). MAO-mediated metabolism of DMT affordsindole-3-acetic acid (IAA) via oxidative deamination (O. Suzuki et al.Inhibition of type A and type B monoamine oxidases by naturallyoccurring xanthones, Planta Med., 42: 17-21 (1981) and J. Riba, et al.,Metabolism and urinary disposition of N,N-dimethyltryptamine after oraland smoked administration: a comparative study, Drug Test. Anal., 7(5):401-406 (2015)).

DMT-N-oxide (DMT-NO) is the second most abundant metabolite of DMTformed via N-oxidation. Further minor metabolites have also beenidentified including N-methyltryptamine (NMT),2-methyl-1,2,3,4-tetrahydro-beta-carboline (MTHBC) and THBC (see Barker(2018), supra, for a review). The production of alternative metabolitessuch as DMT-NO and NMT are believed to be independent of MAO activity(S. A. Barker et al., In vivo metabolism ofα,α,β,β-tetradeutero-N,N-dimethyltryptamine in rodent brain, Biochem.Pharmacol, 33(9): 1395-400 (1984)). It appears unclear as to theresponsible enzyme involved in for the formation of the N-oxide andother metabolites.

In the light of the prominent role understood to be played by MAOs inthe metabolic inactivation by DMT and its substituted analogues, such as5-MeO-DMT, DMT and substituted analogues such as 5-MeO-DMT are oftenadministered with MAO inhibitors (MAOIs) to prevent inactivation of thecompounds before they have reached their target site in the body,allowing for a prolonged and increased exposure to the compound.However, since MAOIs can cause high blood pressure when taken withcertain foods or medications, the use of MAOIs by a patient typicallyrequires the patient to restrict their diet and avoiding some othermedications.

Naturally occurring hydrogen contains about 0.02 molar percent deuteriumand 99.98% protium. Physical chemical properties between protium anddeuterium are small but measurable. Deuterium is slightly lesslipophilic than protium, has a smaller molar volume and carbon-deuteriumbonds are shorter than carbon-protium bonds. Deuterium keeps the 3Dsurface, shape and steric flexibility unaltered compared to H.

These properties indicate that the incorporation of deuterium into DMTis expected to progressively reduce lipophilicity and increase basicityin a non-additive manner, dependent upon stereochemical position, whilstalso retaining the biochemical potency and selectivity of the parentcompound. Moreover, the enrichment of DMT's hydrogen atoms withdeuterium is expected to cause a shift in the compound stability,measured as the deuterium kinetic isotope effect (DKIE).

The difference in stability of isotopically substituted molecules isreferred to as the primary kinetic isotopic effect (KIE), which fordeuterium can be defined as the deuterium kinetic isotope effect (DKIE).DKIE is quantified as the ratio of the rate constants for the reaction(kH/kD) and typically ranges from 1 (where deuterium has no effect onreaction) to 7, with the theoretical limit being 9.

As enzyme-catalysed transformations are multistep, in order to observehigh DKIE, it is necessary that the C—H cleavage step is at leastpartially rate-limiting. Other kinetic models such as quantum-mechanicaltunnelling is invoked to explain a secondary DKIE. While this is usuallymuch smaller in magnitude than the primary effect (typically 1.1-1.2),this mechanism can nonetheless lead to significantly larger effects.

Deuterium substitution of hydrogen atoms at the α and β-positions of theethylamine side chain of DMT (α,α,β,β-tetradeuterio-DMT, D₄DMT) wasdemonstrated by Barker et al. to have a KIE in vivo (S. A. Barker etal., 1982, Comparison of the brain levels of N,N-dimethyltryptamine andα,α,β,β-tetradeutero-N,N-dimethyltryptamine following intraperitonealinjection, Biochemical Pharmacology, 31(15), 2513-2516 (1982)). D₄DMTwas found to have a shorter time to onset and potentiation of behaviourdisrupting effects when compared to equal doses of DMT. However, nokinetic data was reported to quantify the DKIE (S. A. Barker et al.,supra, (1982); S. A. Barker et al., supra (1984); and J. M. Beaton etal., A Comparison of the Behavioral Effects of Proteo- andDeutero-N,N-Dimethyltryptamine. Pharmacol. Biochem. Behav, 1982. 16(5):811-4 (1982)).

The synthesis of α,α,-bis-deuterium-DMT (D₂DMT) has been reported in theliterature (P. E. Morris and C. Chiao (Journal of Labelled Compounds AndRadiopharmaceuticals, Vol. XXXIII, No. 6, 455-465 (1993)). However, nobiological or metabolism data has been published.

In WO 2020/245133 A1 (Small Pharma Ltd), knowledge of the kineticisotope effect exhibited by α,α,β,β-tetradeutero-N,N-dimethyltryptamineis used in order to modify, controllably, the pharmacokinetic profile ofN,N-dimethyltryptamine, thereby permitting more flexible therapeuticapplication.

The use of N,N-(dimethyl-d₆)-tryptamine (d₆-DMT) as an internal standardin the bioanalysis of plasma samples of DMT is described by G. N. Rossiet al., J. Pschedelic Stud., 3(1), 1-6 (2019); G. de Oliveira Silveriaet al., Molecules, 25, 2072, 1-11 (2020); and C. D. R. Oliveira et al.,Bioanalysis, 2012, 4(14), 1731-1738). However, there is no mention ofthe possibility of using d₆-DMT itself as a therapeutically activesubstance.

In light of the therapeutic potential of DMT and substituted analogues,there remains a need in the art for alternative compounds, for examplecompounds with improved bioavailability, extended and/or modifiedpharmacokinetics and/or modified pharmacodynamics, for use inpsychotherapy, in particular for the development of clinicallyapplicable psychedelic drug substances to assist psychotherapy. Thepresent invention addresses this need.

SUMMARY

DMT is metabolised very quickly in the human body. Using modelled datafrom Timmerman (C. Timmermann et al., DMT Models the Near-DeathExperience, Front. Psychol 9: 1424 (2018) and C. Timmermann et al.,Neural correlates of the DMT experience assessed with multivariate EEG,Sci. Rep. 9: 16324 (2019)), we have calculated that DMT has have ahalf-life of approximately 5 minutes and clearance rate of 24483 ml/min,which equates to 350 ml/min/kg based on a 70 kg person. This clearancerate is much greater than average human liver blood flow, which is 20ml/min/kg with a cardiac output of 71 ml/min/kg. Based on thesecalculations, we reasoned that DMT is largely metabolised beforereaching the human liver.

In research described herein, we have demonstrated that intrinsicclearance and half-life values of deuterated DMT compounds in humanliver mitochondrial fractions, which contain high quantities of MAOs,are different to the values in hepatocytes such as human livermicrosomes and whole cell hepatocytes. Moreover, these pharmacodynamicparameters vary additionally depending on whether there is deuteriumsubstitution at the carbon atom adjacent to the dimethylamino moiety ofDMT (α-deuteration) or on the carbon atoms of the methyl groups (methylgroup deuteration).

Specifically, we found that α-deuteration gives rise to an increase inmetabolic stability (in comparison with the parent compound:undeuterated DMT) in human hepatocytes whereas methyl group deuterationhas a minimal effect on metabolic stability in such a system. On theother hand, significantly greater increases in metabolic stability inmitochondrial fractions were found with a representative deuterated DMThaving complete methyl group deuteration in comparison with acorresponding compound with no methyl group deuteration.

The liver contains both phase I and phase II drug metabolising enzymes,which are present in the intact cell, making hepatocytes a valuable invitro model for the study of drug metabolism, in order to predict invivo clearance. However, hepatic fractions such as human livermicrosomes and whole cell hepatocytes contain significant quantities ofcytochrome P450 enzymes, the predominant location of cytochrome P450enzymes in the body being in the liver. Human liver mitochondrialfractions, although being liver-derived, contain less cytochrome P450enzymes than whole cell hepatocytes but, as already noted, significantquantities of MAOs. Whilst whole cell hepatocytes also containsignificant quantities of MAOs, MAO is more homogeneously distributedthroughout the body (more homogeneously than cytochrome P450 enzymesthat is), being found in most cell types.

The enhancement in metabolic stability in human liver mitochondrialfractions conferred by methyl group deuteration is suggestive of agreater stability towards metabolism by mitochondrial enzymes, and thusof greater metabolic stability in vivo, in comparison with undeuteratedor alpha-only deuterated DMT.

Accordingly, and viewed from a first aspect, the invention provides acompound of formula (I):

wherein:

-   -   R¹ is independently selected from —R⁴, —OH, —OR⁴, —O(CO)R⁴,        monohydrogen phosphate, —F, —Cl, —Br and —I;    -   n is selected from 0, 1, 2, 3 or 4;    -   R² is C(^(x)H)₃;    -   R³ is C(^(x)H)₃ or H;    -   each R⁴ is independently selected from C₁-C₄alkyl; and    -   each ^(x)H and ^(y)H is independently protium or deuterium,    -   wherein a ratio of deuterium:protium in a C(^(x)H)₃ moiety in        the compound is greater than that found naturally in hydrogen,    -   or a pharmaceutically acceptable salt thereof,    -   for use in therapy.

It is understood that the only DMT compound with methyl groupdeuteration described hitherto is N,N-di(trideuteromethyl)tryptamine(i.e. d₆-DMT) with no suggestion in the art of the utility of methylgroup deuteration in providing therapeutically active DMTs. Accordingly,viewed from a second aspect, the invention provides a compound orpharmaceutically acceptable salt is defined in accordance with the firstaspect of the invention, which is notN,N-di(trideuteromethyl)tryptamine, but which may, for example, be apharmaceutically acceptable salt of N,N-di(trideuteromethyl)tryptamine.

Viewed from a third aspect, the invention provides a compositioncomprising a first compound, which is a compound or pharmaceuticallyacceptable salt thereof as defined in accordance with the first aspectof the invention, and a second compound, which is either (i) a compoundor pharmaceutically acceptable salt thereof as defined in accordancewith the first aspect of the invention, but which differs from the firstcompound through the identity of ^(y)H and/or the identity of R³; or(ii) a compound or pharmaceutically acceptable salt thereof as definedin accordance with the first aspect of the invention, except that each^(x)H and ^(y)H represent hydrogen.

Viewed from a fourth aspect, the invention provides a pharmaceuticalcomposition comprising a compound defined in accordance with the firstor second aspects of the invention or composition in accordance with thethird aspect of the invention, in combination with a pharmaceuticallyacceptable excipient.

Viewed from a fifth aspect, the invention provides a compound defined inaccordance with the first or second aspects of the invention orcomposition in accordance with the third or fourth aspects of theinvention for use in a method of treating a psychiatric or neurologicaldisorder in a patient.

Viewed from a sixth aspect, the invention provides a method of treatmentcomprising administering to a patient in need thereof a compound definedin accordance with the first or second aspects of the invention orcomposition in accordance with the third or fourth aspects of theinvention.

Viewed from a seventh aspect, the invention provides a method comprisingsynthesising a compound of formula (I′):

or a pharmaceutically acceptable salt thereof, comprising reacting acompound of formula (II):

with LiAlH₄ and/or LiAlD₄, wherein:

-   -   R^(1′) is independently selected from —R⁴, —OPR, —OR⁴, —F, —Cl,        —Br and —I;    -   PR is a protecting group,    -   n is selected from 0, 1, 2, 3 or 4;    -   R² is C(^(x)H)₃;    -   R³ is C(^(x)H)₃ or H;    -   each R⁴ is independently selected from C₁-C₄alkyl; and    -   each ^(x)H and ^(y)H is independently protium or deuterium,    -   wherein a ratio of deuterium:protium in a C(^(x)H)₃ moiety in        the compound of formula (I′) is greater than that found        naturally in hydrogen,    -   or a pharmaceutically acceptable salt thereof.

Optionally, compounds of formula (I′) in which R^(1′) is —OPR areconverted to compounds of formula (I) using chemistry at the disposal ofthe skilled person.

Further aspects and embodiments of the present invention will be evidentfrom the discussion that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : calculated in vitro half-life for DMT and 6deuterium-containing compositions, as described in the Examples section,below. A) Linear regression analysis. The r² value for half-life is0.754; where the slope was found to be significantly different to zero,p=0.01. B) Half-life of deuterated analogues as a percent change from(undeuterated) DMT (dashed line).

FIG. 2 : In vitro intrinsic clearance (A) and half-life (B) of DMT(SPL026) and 6 different D₂-deuterated SPL028 analogue blends in humanhepatocytes with and without MAO-A/B inhibitor combination, as describedin the Example section, below.

DETAILED DESCRIPTION

Throughout this specification, one or more aspects of the invention maybe combined with one or more features described in the specification todefine distinct embodiments of the invention.

In the discussion that follows, reference is made to a number of terms,which are to be understood to have the meanings provided below, unless acontext expressly indicates to the contrary. The nomenclature usedherein for defining compounds, in particular the compounds describedherein, is intended to be in accordance with the rules of theInternational Union of Pure and Applied Chemistry (IUPAC) for chemicalcompounds, specifically the “IUPAC Compendium of Chemical Terminology(Gold Book)” (see A. D. Jenkins et al., Pure & Appl. Chem., 1996, 68,2287-2311). For the avoidance of doubt, if a rule of the IUPACorganisation is contrary to a definition provided herein, the definitionherein is to prevail.

References herein to a singular of a noun encompass the plural of thenoun, and vice-versa, unless the context implies otherwise. For example,“a compound of formula (I)” refers to one or more compounds of formula(I).

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps. The term “comprising” includeswithin its ambit the term “consisting”.

The term “consisting” or variants thereof is to be understood to implythe inclusion of a stated element, integer or step, or group ofelements, integers or steps, and the exclusion of any other element,integer or step or group of elements, integers or steps.

The term “about” herein, when qualifying a number or value, is used torefer to values that lie within ±5% of the value specified. For example,if a temperature range of about 15 to about 25° C. is referred to,temperatures of 14.25 to 26.25° C. are encompassed.

The term “hydrocarbyl” defines univalent groups derived fromhydrocarbons by removal of a hydrogen atom from any carbon atom, whereinthe term “hydrocarbon” refers to compounds consisting of hydrogen andcarbon only. Where a hydrocarbyl is disclosed as optionally comprisingone or more heteroatoms, any carbon or hydrogen atom on the hydrocarbylmay be substituted with a heteroatom or a functional group comprising aheteroatom, provided that valency is satisfied. One or more heteroatomsmay be selected from the group consisting of nitrogen, sulfur andoxygen.

Oxygen and sulfur heteroatoms or functional groups comprising theseheteroatoms may replace —H or —CH₂— of a hydrocarbyl, provided that,when —H is replaced, oxygen or the functional group comprising oxygenbinds to the carbon originally bound to the —H as either ═O (replacingtwo —H) or —OH (replacing one —H), and sulfur or the functional groupcomprising sulfur binds to the carbon atom originally bound to the —H aseither ═S (replacing two —H) or —SH (replacing one —H). When methylene(—CH₂—) is replaced, oxygen binds to the carbon atoms originally boundto —CH₂— as —O— and sulfur binds to the carbon atoms originally bound to—CH₂— as —S—.

Nitrogen heteroatoms or functional groups comprising nitrogenheteroatoms may replace —H, —CH₂—, or —CH═, provided that, when —H isreplaced, nitrogen or the functional group comprising nitrogen binds tothe carbon originally bound to the —H as ≡N (replacing three —H), ═NH(replacing two —H) or —NH₂ (replacing one —H); when —CH₂— is replaced,nitrogen or the functional group comprising nitrogen binds to the carbonatoms originally bound to —CH₂— as —NH—; and when —CH═ is replaced,nitrogen binds to the carbon atoms originally bound to —CH═ as —N═.

The term “alkyl” is well known in the art and defines univalent groupsderived from alkanes by removal of a hydrogen atom from any carbon atom,wherein the term “alkane” is intended to define acyclic branched orunbranched hydrocarbons having the general formula C_(n)H_(2n+2),wherein n is an integer ≥1. C₁-C₄alkyl refers to any one selected fromthe group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl,sec-butyl, iso-butyl and tert-butyl.

The term “cycloalkyl” defines all univalent groups derived fromcycloalkanes by removal of a hydrogen atom from a ring carbon atom. Theterm “cycloalkane” defines saturated monocyclic and polycyclic branchedor unbranched hydrocarbons, where monocyclic cycloalkanes have thegeneral formula C_(n)H_(2n), wherein n is an integer ≥3. Typically, thecycloalkyl is a C₅-C₆cycloalkyl, such as cyclopentyl or cyclohexyl.

The term “alkylamino” refers to alkyl groups in which any one hydrogenatom is substituted with a primary (—NH₂), secondary (—NRH) or tertiary(—NR₂) amino groups, where R is, or each R is independently, ahydrocarbyl group. Typically, any one hydrogen atom is substituted witha tertiary amino group wherein each R is independently a C₁-C₄alkyl.

The term “acetoxy” (often abbreviated to OAc) defines a univalent groupderived from acetic acid by removal of a hydrogen atom from the OHmoiety. The term “methoxy” (often abbreviated to OMe) defines aunivalent group derived from methanol by removal of a hydrogen atom fromthe OH moiety. The term monhydrogen phosphate defines a divalent groupof formula HPO₄, derived from phosphoric acid by removal of a protonfrom two of the three OH moieties, and thus denotes a substituent offormula —OP(O)(OH)O⁻.

By hydrogen is meant herein that, in a plurality of like compounds, theisotopes of such denoted hydrogen are present in their naturalabundances unless a context explicitly dictates to the contrary. Forexample, where ^(x)H and ^(y)H in a particular compound are stated torepresent hydrogen, the isotopes of hydrogen in ^(x)H and ^(y)H in aplurality of such compounds are present in their natural abundances.

Where a compound, for example of formula (I), is substituted withmonohydrogen phosphate (i.e. where R¹ is monohydrogen phosphate), it isunderstood that “monohydrogen phosphate” also encompasses protonated orunprotonated analogues, i.e. dihydrogen phosphate and phosphate are alsoincluded. This is to reflect that psilocybin (also known as[3-(2-Dimethylaminoethyl)-1H-indol-4-yl] dihydrogen phosphate), andanalogues such as [3-(2-methylaminoethyl)-1H-indol-4-yl] dihydrogenphosphate, in water generally comprise monohydrogen phosphate, thisgenerally being understood to be the predominant form owing to the pKavalues of the two terminal phosphate oxygen atoms being estimated as 1.3and 6.5. It is further understood that the monohydrogenphosphate-containing form of psilocybin and analogues exists as azwitterion (i.e. an internal salt) in which the nitrogen atom of thedimethylamino (or monomethylamino) moiety is protonated. For theavoidance of doubt, zwitterions are considered separately to salts, i.e.the pharmaceutically acceptable salts of the invention refer to saltscomprising compounds of formula (I) of the invention and an acid. Forexample, a salt may be of psilocybin and fumaric acid.

The compounds of formula (I) described herein, for example within thecompositions in accordance with the third and fourth aspects of theinvention, are useful in therapy and may be administered to a patient inneed thereof. As used herein, the term ‘patient’ preferably refers to amammal. Typically, the mammal is a human, but may also refer to adomestic mammal. The term does not encompass laboratory mammals.

The terms “treatment” and “therapy” define the therapeutic treatment ofa patient, in order to reduce or halt the rate of progression of adisorder, or to ameliorate or cure the disorder. Prophylaxis of adisorder as a result of treatment or therapy is also included.References to prophylaxis are intended herein not to require completeprevention of a disorder: its development may instead be hinderedthrough treatment or therapy in accordance with the invention.Typically, treatment or therapy is not prophylactic, and the compoundsor compositions are administered to a patient having a diagnosed orsuspected disorder.

Psychedelic-assisted psychotherapy means the treatment of a mentaldisorder by psychological means, which are enhanced by one or moreprotocols in which a patient is subjected to a psychedelic experience. Apsychedelic experience is characterized by the striking perception ofaspects of one's mind previously unknown, and may include one or morechanges of perception with respect to hallucinations, synesthesia,altered states of awareness or focused consciousness, variation inthought patterns, trance or hypnotic states, and mystical states.

As is understood in the art, psychocognitive, psychiatric orneurological disorders are disorders which may be associated with one ormore cognitive impairment. As used herein, the term ‘psychiatricdisorder’ is a clinically significant behavioural or psychologicalsyndrome or pattern that occurs in an individual and that is associatedwith present distress (e.g., a painful symptom) or disability (i.e.,impairment in one or more important areas of functioning) or with asignificantly increased risk of suffering death, pain, disability, or animportant loss of freedom.

Diagnostic criteria for psychiatric or neurological disorders referredto herein are provided in the Diagnostic and Statistical Manual ofMental Disorders, Fifth Edition, (DSM-5).

As used herein the term ‘obsessive-compulsive disorder’ (OCD) is definedby the presence of either obsessions or compulsions, but commonly both.The symptoms can cause significant functional impairment and/ordistress. An obsession is defined as an unwanted intrusive thought,image or urge that repeatedly enters the person's mind. Compulsions arerepetitive behaviours or mental acts that the person feels driven toperform. Typically, OCD manifests as one or more obsessions, which driveadoption of a compulsion. For example, an obsession with germs may drivea compulsion to clean or an obsession with food may drive a compulsionto overeat, eat too little or throw up after eating (i.e. an obsessionwith food may manifest itself as an eating disorder). A compulsion caneither be overt and observable by others, such as checking that a dooris locked, or a covert mental act that cannot be observed, such asrepeating a certain phrase in one's mind.

The term “eating disorder” includes anorexia nervosa, bulimia and bingeeating disorder (BED). The symptoms of anorexia nervosa include eatingtoo little and/or exercising too much in order to keep weight as low aspossible. The symptoms of bulimia include eating a lot of food in a veryshort amount of time (i.e. binging) and then being deliberately sick,using laxatives, eating too little and/or exercising too much to preventweight gain. The symptoms of BED include regularly eating large portionsof food until uncomfortably full, and consequently feeling upset orguilty.

As used herein the term ‘depressive disorder’ includes major depressivedisorder, persistent depressive disorder, bipolar disorder, bipolardepression, and depression in terminally ill patients.

As used herein the term ‘major depressive disorder’ (MDD, also referredto as major depression or clinical depression) is defined as thepresence of five or more of the following symptoms over a period oftwo-weeks or more (also referred to herein as a ‘major depressiveepisode’), most of the day, nearly every day:

-   -   depressed mood, such as feeling sad, empty or tearful (in        children and teens, depressed mood can appear as constant        irritability);    -   significantly reduced interest or feeling no pleasure in all or        most activities;    -   significant weight loss when not dieting, weight gain, or        decrease or increase in appetite (in children, failure to gain        weight as expected);    -   insomnia or increased desire to sleep;    -   either restlessness or slowed behaviour that can be observed by        others;    -   fatigue or loss of energy;    -   feelings of worthlessness, or excessive or inappropriate guilt;    -   trouble making decisions, or trouble thinking or concentrating;    -   recurrent thoughts of death or suicide, or a suicide attempt.        At least one of the symptoms must be either a depressed mood or        a loss of interest or pleasure.

Persistent depressive disorder, also known as dysthymia, is defined as apatient exhibiting the following two features:

-   -   A. has depressed mood for most the time almost every day for at        least two years. Children and adolescents may have irritable        mood, and the time frame is at least one year.    -   B. While depressed, a person experiences at least two of the        following symptoms:        -   Either overeating or lack of appetite.        -   Sleeping too much or having difficulty sleeping.        -   Fatigue, lack of energy.        -   Poor self-esteem.        -   Difficulty with concentration or decision-making.

As used herein the term ‘treatment resistant major depressive disorder’describes MDD that fails to achieve an adequate response to an adequatetreatment with standard of care therapy.

As used herein, ‘bipolar disorder’, also known as manic-depressiveillness, is a disorder that causes unusual shifts in mood, energy,activity levels, and the ability to carry out day-to-day tasks.

There are two defined sub-categories of bipolar disorder; all of theminvolve clear changes in mood, energy, and activity levels. These moodsrange from periods of extremely “up,” elated, and energised behaviour(known as manic episodes, and defined further below) to very sad,“down,” or hopeless periods (known as depressive episodes). Less severemanic periods are known as hypomanic episodes.

Bipolar I Disorder—defined by manic episodes that last at least 7 days,or by manic symptoms that are so severe that the person needs immediatehospital care. Usually, depressive episodes occur as well, typicallylasting at least 2 weeks. Episodes of depression with mixed features(having depression and manic symptoms at the same time) are alsopossible.

Bipolar II Disorder—defined by a pattern of depressive episodes andhypomanic episodes, but not the full-blown manic episodes describedabove.

As used herein ‘bipolar depression’ is defined as an individual who isexperiencing depressive symptoms with a previous or coexisting episodeof manic symptoms, but does not fit the clinical criteria for bipolardisorder.

As used herein, the term ‘anxiety disorder’ includes generalised anxietydisorder, phobia, panic disorder, social anxiety disorder, andpost-traumatic stress disorder.

‘Generalised anxiety disorder’ (GAD) as used herein means a chronicdisorder characterised by long-lasting anxiety that is not focused onany one object or situation. Those suffering from GAD experiencenon-specific persistent fear and worry, and become overly concerned witheveryday matters. GAD is characterised by chronic excessive worryaccompanied by three or more of the following symptoms: restlessness,fatigue, concentration problems, irritability, muscle tension, and sleepdisturbance.

‘Phobia’ is defined as a persistent fear of an object or situation theaffected person will go to great lengths to avoid, typicallydisproportional to the actual danger posed. If the feared object orsituation cannot be avoided entirely, the affected person will endure itwith marked distress and significant interference in social oroccupational activities.

A patient suffering from a ‘panic disorder’ is defined as one whoexperiences one or more brief attack (also referred to as a panicattack) of intense terror and apprehension, often marked by trembling,shaking, confusion, dizziness, nausea, and/or difficulty breathing. Apanic attack is defined as a fear or discomfort that abruptly arises andpeaks in less than ten minutes.

‘Social anxiety disorder’ is defined as an intense fear and avoidance ofnegative public scrutiny, public embarrassment, humiliation, or socialinteraction. Social anxiety often manifests specific physical symptoms,including blushing, sweating, and difficulty speaking.

‘Post-traumatic stress disorder’ (PTSD) is an anxiety disorder thatresults from a traumatic experience. Post-traumatic stress can resultfrom an extreme situation, such as combat, natural disaster, rape,hostage situations, child abuse, bullying, or even a serious accident.Common symptoms include hypervigilance, flashbacks, avoidant behaviours,anxiety, anger and depression.

As used herein, the term “post-partum depression” (PPD, also known aspostnatal depression) is a form of depression experienced by eitherparent of a newborn baby. Symptoms typically develop within 4 weeks ofdelivery of the baby and often include extreme sadness, fatigue,anxiety, loss of interest or pleasure in hobbies and activities,irritability, and changes in sleeping or eating patterns.

As used herein, the term ‘substance abuse’ means a patterned use of adrug in which the user consumes the substance in amounts or with methodsthat are harmful to themselves or others.

As used herein, the term ‘an avolition disorder’ refers to a disorderthat includes as a symptom the decrease in motivation to initiate andperform self-directed purposeful activities.

In its various aspects, the invention relates to compounds of formula(I). The compounds of formula (I) (and as well as each of the compoundsof formulae (I′), (II) and N(H)R²R³ described herein) comprise aC(^(x)H)₃ moiety (and in some embodiments two such moieties) in whichthe ratio of deuterium:protium is greater than its natural isotopicabundance, i.e. the compound concerned comprises a methyl group in whichthe percentage of deuterium amongst the hydrogen atoms in the compoundsof the formula is greater than its natural isotopic abundance inhydrogen, which is about 0.02 mol %.

In the compounds of formula (I), in accordance with particularembodiments of at least the first to sixth aspects of the invention, R¹is independently selected from —OR⁴, —O(CO)R⁴, monohydrogen phosphateand —OH. In particular embodiments of these and other embodiments, R⁴ ismethyl.

Sometimes, in the compounds of formulae (I), (I′) and (II) (formulae(I′) and (II) being described infra), in accordance with any relevantaspect or embodiment of the invention, n is 0 or 1. According to someembodiments, n is 0.

Where n is 1, R¹ (or R^(1′), in compounds of formulae (I′) and (II)) isat the 4- or 5-position. For the avoidance of doubt, positions 4 and 5refer to these positions with represents to the labelled structure ofDMT depicted below:

According to some embodiments, In the compounds of formula (I), inaccordance with particular embodiments of at least the first to sixthaspects of the invention, n is 0, or n is 1 and R¹ is selected from5-methoxy, 5-bromo, 4-acetoxy, 4-monohydrogen phosphate, 4-hydroxy and5-hydroxy.

According to some embodiments of all aspects of the invention, n is 0,or n is 1 and R¹, or as appropriate R^(1′), is 5-methoxy.

Sometimes, in the compounds described herein having ^(y)H moieties,these are deuterium (that is to say hydrogen in which the proportion ofdeuterium has been increased beyond its natural abundance); sometimesthese ^(y)H moieties are protium (that is to say hydrogen in which theproportion of deuterium has not been increased beyond its naturalabundance).

For the avoidance of doubt, by a ^(x)H or ^(y)H being deuterium is meantthat the atom concerned is enriched with deuterium, i.e. the hydrogenatoms of the resultant compound by virtue of this enrichment comprises agreater percentage of deuterium than that found naturally in hydrogen,which is about 0.02 mol %.

Where compounds described herein are indicated as being or described assubstituted with deuterium, the compound concerned is enriched withdeuterium by an amount that is dependent on the percentage of deuteriumavailable in the reagents from which the compounds are derived. Forexample, and as described herein, the d₆-dimethylamino ord₃-monomethylamino portions of compounds of formulae (I), (I′) and (II),wherein —NR²R³ is —N(CD₃)₂ and —N(H)CD₃ respectively, may be derivedfrom dimethyl-d₇-amine, dimethyl-d₆-amine or methyl-d₃-amine (commonlyavailable as HCl salts), which are available from chemical vendors inpurities of deuterium that range from 98% to 99%. The purity ofdeuterium in the resultant d₆-dimethylamino or d₃-monomethylaminosubstituents is consequently between 98% and 99%. This means, as theskilled person will understand, that not all compounds of formula (I)(for example) will comprise d₆-dimethylamino or d₃-monomethylaminosubstituents—some may comprise d₀-d₅dimethylamino ord₀-d₃-monomethylamino substituents, but the average purity of deuteriumis about 98% to 99%.

Sometimes, in the relevant compounds described herein, R² and R³ areboth C(^(x)H)₃, and in some of these embodiments both C(^(x)H)₃ are thesame. According to particular embodiments, both R² and R³ are CD₃.

In accordance with the second aspect of the invention, there is provideda compound of formula (I), with the proviso that this is notN,N-di(trideuteromethyl)tryptamine. The compound of the invention can,however, be a pharmaceutically acceptable salt ofdi(trideuteromethyl)tryptamine, for exampledi(trideuteromethyl)tryptamine fumarate; or otherN,N-di(trideuteromethyl)tryptamines of formula (I), for example5-methoxy,N,N-di(trideuteromethyl)tryptamine or a pharmaceuticallyacceptable salt thereof.

Compounds of formula (I), including the particular embodiments justdescribed (including those in which n=0 and n=1, wherein R¹ is5-methoxy) can, for example, be synthesised by following the reactionscheme set out in Scheme 1 below:

Scheme 1 depicts the synthesis of compounds of formula (I) in which n=0.Variations of the chemistry described (relevant for example to thesynthesis of compounds of formula (I) in which n is other than 0) arewell within the normal ability of a skilled person, using his or hercommon general knowledge and/or the teaching herein.

The chemistry depicted in Scheme 1 was reported by P. E. Morris and C.Chiao (supra). Deuterated compounds of or used in accordance with thevarious aspects of the invention, or indeed undeuterated compoundsrelevant to the present invention, which may be useful in embodiments ofthe third to sixth aspects of the invention as described herein, canalso be synthesised following the chemistry depicted in Scheme 2, orvariations of this chemistry.

As with Scheme 1, Scheme 2 depicts the synthesis of compounds of formula(I) in which n=0. Carrying out the chemistry described in this Schemeand variations thereof (discussed extensively below with regard to theseventh aspect of the invention) is well within the normal ability of askilled person.

It will be understood that the formation of fumarate salts as depictedin Stage 3 of Scheme 2 may be varied to afford other pharmaceuticallyacceptable salts and that this salt formation step can also be carriedout on the final product(s) depicted in Scheme 1.

Relative amounts of protium to deuterium as ^(y)H in the compoundssynthesised may be controlled by varying the ratio of lithium aluminiumhydride and lithium aluminium deuteride as the reducing agent (see forexample WO 2020/245133 A1 (Small Pharma Ltd), supra). The proportion ofprotium and deuterium at these positions may be further varied ifdesired, for example to provide compositions according to the inventionin a controllable way, by adding one or more of the protio or deuterocompounds to the compositions described herein.

It will be seen from Scheme 1 that step (ii), and from Scheme 2 thatStage 1, serves to effect introduction of the amine moiety (—NR²R³) intothe compounds. It will be understood that the synthesis of compounds offormula (I), which comprise at least one C(^(x)H)₃ moiety in which thepercentage of deuterium is greater than its natural isotopic abundancein hydrogen, may be achieved through the use of appropriate deuteratedmonomethylamines and dimethylamines, which are commercially available.In particular, use of commercially available d₇-dimethylamine (i.e.DN(CD₃)₂), d₆-dimethylamine (i.e. di(trideuteromethyl)amine) andd₃-methylamine (i.e. trideuteromethylamine) allow access to compounds offormula (I), and in accordance with the seventh aspect of the invention,compounds of formula (I′), in which —NR²R³ is —N(CD₃)₂ and —N(H)CD₃.

Identification of the compositions resultant from the reduction step inSchemes 1 and 2 may be achieved, if desired, by chromatographicseparation of the components of the mixtures by conventional means atthe disposal of the skilled person, in combination with spectroscopicand/or mass spectrometric analysis.

Alternative compositions are obtainable by mixing undeuteratedcompounds, obtainable by Scheme 1 or Scheme 2 when the reducing agent isexclusively lithium aluminium hydride, with an α,α-dideutero compoundobtainable from Scheme 1 or Scheme 2 when the reducing agent isexclusively lithium aluminium deuteride, it being understood whenreference is made to reducing agents being exclusively lithium aluminiumhydride or lithium aluminium deuteride that this refers to an ideal, andis ultimately subject to the purity of the reagent concerned, asdiscussed above.

The compositions described hereinabove may be further modified by addingone or more α-monodeutero compounds. Stocks of such compounds may beobtained, for example, from the chromatographic separation describedabove.

Scheme 3 depicts chemistry based on that known in the art forsynthesising DMT, which may be deployed/modified to synthesise compoundsof formula (I), in which substituent R¹ denotes hydrogen (i.e. whereinn=0) or the substituent R¹ as defined herein, and R² and R³ are asdefined herein. Whilst typically no more than one R¹ group will bepresent, pluralities of R¹ moieties are not excluded.

As with Schemes 1 and 2, Scheme 3 illustrates how the amine moiety(—NR²R³) is introduced into the compounds and how, in step (iii),relative proportions of protium to deuterium in the compounds (i.e. theconstitution of substituents ^(y)H) may be controlled by varying theratio of lithium aluminium hydride and lithium aluminium deuteride (seeagain, for example, WO 2020/245133 A1 (Small Pharma Ltd), supra). Step(iv) may be used to introduce C(^(x)H)₃ moieties as R² and R³ in whichthe amount of deuterium may be controlled through the use of mixtures ofsodium borohydride and sodium borodeuteride or sodium borodeuteride(see, for example, the synthesis of DMT-d6 described by Oliveira et al.(supra).

Tryptamines are generally synthesised using methods adapted fromAlexander Shulgin's pioneering publication TiHKAL: The Continuation(Berkeley, Calif., Transform Press, 1997). This discloses severalalternative methods for synthesising DMT; the three step route startingfrom indole using (1) oxalyl chloride, (2) dimethylamine and (3) lithiumaluminium hydride has been widely adopted (see top synthetic routedepicted in Scheme 3), and analogous routes have been used to scalepsilocybin under GMP controls (see, for example, WO 2019/073379 A1).Oxalyl chloride is very toxic and corrosive. It is severely irritatingto eyes, skin, and the respiratory tract and reacts violently with watermaking it difficult to handle at scale.

The synthesis of DMT from auxin (a plant hormone and natural product,and the compound depicted first in both Schemes 1 and 2) has beenreported by P. E. Morris and C. Chiao, supra (see again Scheme 1 andalso the bottom synthetic route depicted in Scheme 3 (steps (vi), (vii)then (iii)). Whilst it is possible to use the oxalyl chloride route tomake compounds of formula (I), an advantageous feature of the presentinvention is the avoidance of this and the provision of high-puritycompounds of formula (I) without sacrificing yield. This is thechemistry depicted in Scheme 2, to which the seventh aspect of theinvention relates, and which can be modified to provide R¹-containingcompounds of formula (I) through the use of R¹-containing startingmaterials (or R^(1′)-containing starting materials), for example bymodifying the chemistry described in Scheme 2 with the use of protectinggroups, also described herein.

In particular, and in accordance with the seventh aspect of theinvention, there is provided a method comprising synthesising a compoundof formula (I′):

or a pharmaceutically acceptable salt thereof, comprising reacting acompound of formula (II):

with LiAlH₄ and/or LiAlD₄, wherein:

-   -   R^(1′) is independently selected from —R⁴, —OPR, —OR⁴, —F, —Cl,        —Br and —I;    -   PR is a protecting group,    -   n is selected from 0, 1, 2, 3 or 4;    -   R² is C(^(x)H)₃;    -   R³ is C(^(x)H)₃ or H;    -   each R⁴ is independently selected from C₁-C₄alkyl; and    -   each ^(x)H and ^(y)H is independently protium or deuterium,    -   wherein a ratio of deuterium:protium in a C(^(x)H)₃ moiety in        the compound of formula (I′) is greater than that found        naturally in hydrogen,    -   or a pharmaceutically acceptable salt thereof.

It will be understood that the reduction of the amide carbonyl group incompounds of formula (II) corresponds to Stage 2 in Scheme 2 and thatoptional substituent(s) R^(1′) in the compounds of formulae (I′) and(II) may be present.

In the compounds of formulae (I′) and (II), PR is a protecting group. Inother words, where an R^(1′) group represents OPR, this denotes aprotected hydroxyl group. The skilled person is well aware that duringsynthetic sequences it may be advantageous to protect sensitive orreactive groups on any of the molecules concerned. This is achieved bymeans of protecting groups, a concept with which the skilled person iscompletely familiar. Suitable protecting groups and the ways in whichthese may be used are described, for example, by T. W. Greene and P. G.M. Wutts in ‘Protective Groups in Organic Synthesis’ 5^(th) Edition,John Wiley and Sons, 2014.

When a compound of formula (I′) is made with a —OPR group, this may be,and typically will be, removed after the reduction of the compound offormula (II) described in accordance with the method of the seventhaspect of the invention, using deprotection methods well known in theart (see again T. W. Greene and P. G. M. Wutts, supra). The hydroxylgroup thereby revealed may be converted if desired into a —OR⁴,—O(CO)R⁴, or monohydrogen phosphate moiety (as defined herein). Suchreactions represent particular embodiments of the seventh aspect of theinvention.

According to such embodiments, the method of the seventh aspect of theinvention further comprises, where a compound of formula (I′) comprisesa —OPR group, removing the protecting group and optionally (buttypically) converting the resultant —OH group to a —OR⁴, —O(CO)R⁴, ormonohydrogen phosphate moiety.

For example, to synthesise compounds of formula (I) having hydroxy,monohydrogen phosphate or acetyl substituents, a benzyloxy2-(3-indolyl)-oxoacetamide having suitable R² and R³ groups may bereduced with a desired ratio of lithium aluminium hydride and lithiumaluminium deuteride to produce a benzyloxy-N,N-dimethyl tryptamine(optionally substituted once or twice at the α position with deuterium).The benzyl protecting group may then be removed, e.g. by hydrogenatingwith hydrogen and palladium on carbon, to form the correspondinghydroxy-tryptamine (optionally substituted at the α position withdeuterium). The hydroxy group may be converted to a monohydrogenphosphate or an acetyl by reaction with eithertetra-O-benzyl-pyrophosphate (followed by removal of the benzylprotecting group) or reaction with acetic anhydride (or other acidanhydride, acyl halide or other method of converting the —OH group to a—O(CO)R⁴ moiety). See D. E. Nichols and S. Frescas, Synthesis, 1999, 6,935-938 for further information on this synthetic strategy.

According to particular embodiments of the method of the seventh aspectof the invention, R1′ in formulae (I′) and (II) is not OPR, i.e. isindependently selected from —R⁴, —OR⁴, —F, —Cl, —Br and —I, thecompounds of formula (I′) according to such embodiments representing asubset of the compounds of formula (I) defined in accordance with thefirst aspect of the invention. According to even more specificembodiments of the method of the seventh aspect of the invention,including the embodiments described below, there is no R^(1′)substituent (i.e. n=0) or R^(1′) is 5-OMe.

In Scheme 2, Stage 1 comprises reacting the depicted carboxylic acidreactant with two or more coupling agents to produce an activatedcompound and reacting the activated compound with an amine to producethe amide depicted. Stage 2 comprises reacting the amide with LiAlH₄and/or LiAlD₄ and corresponds to the method of the seventh aspect of theinvention. Stage 3 depicts optional salt formation. Wheredesired/appropriate, any deprotection (removal) of a protecting groupand conversion as immediately hereinbefore described will typically takeplace after Stage 2 and before Stage 3.

Advantageously, the method of the seventh aspect of the invention avoidsthe use of problematic oxalyl chloride and employs starting materialsthat may be derived from auxin (indole-3-acetic acid). High quality andpure auxins (derivatives of the carboxylic acid starting materialdepicted in Scheme 2 (comprising substituent(s) R^(1(′)) arecommercially available at scale and/or can be readily synthesised viathe Fischer synthesis, Bartoli synthesis, Japp-Klingemann synthesis orLarock synthesis (see, for example, M. B. Smith and J. March, 2020,March's Advanced Organic Chemistry, 8^(th) edition, Wiley, N.J.).

The method of Scheme 2, which represents an exemplary, specificembodiment of the seventh aspect of the invention is efficient,scalable, compatible with Current Good Manufacturing Practices (cGMP),and is suitable for the production of high purity compounds of formula(I). For example, the method is suitable for the production of compoundsof formula (I) in batch scales ranging from 1 g to 100 kg and issuitable for the production of compounds of formula (I) with a purityof >99.9% and overall yield of 50% or more.

It will be understood from the foregoing discussion that, according toparticular embodiments, the method of the seventh aspect of theinvention may further comprise making the compound of formula (II) by:

-   -   (i) reacting a compound of formula (III)

-   -    wherein R^(1′) and n are as defined for formula (I′), with two        or more coupling agents to produce an activated compound; and    -   (ii) reacting the activated compound with an amine having the        formula R²R³NH or R²R³ND, the definitions of n, R^(1′), R² and        R³ corresponding to those in the compound of formula (II).

It will be understood that the starting material depicted in Scheme 2 isan example of a compound of formula (III) in which n=0.

Typically, n herein will be 0 or 1, often (but by no means necessarily)0. Examples of suitable starting materials of formula (III) where n is 1are, for example, include 4- and 5-hydroxyindole acetic acid.

For the avoidance of doubt, where a reagent is expressed herein as anumber of equivalents, this is with respect to the molar equivalents ofthe reactant compounds of for reagents in Stages 1 to 3 of Scheme 2.

The term “coupling agent” refers to an agent which facilitates thechemical reaction between an amine and a carboxylic acid. In someembodiments, the two or more coupling agents comprise a carboxylic acidactivating agent, i.e. an agent which reacts with the carboxylic acidmoiety in Stage 1 (i.e. in compounds of formula (III)) to produce acompound comprising an activated moiety derived from the originalcarboxylic acid moiety, which is more likely to react with an amine thanthe original carboxylic acid moiety.

An additive coupling agent (also referred to herein as an “additive”) isan agent which enhances the reactivity of a coupling agent. In someembodiments, the additive is a compound capable of reacting with theproduct of the reaction of the starting carboxylic acid and the couplingagent (the product being a compound comprising an activated moiety) toproduce a compound comprising an even more activated moiety that is morelikely to react with an amine than the original activated moiety.

Unless a context indicates otherwise, amine means secondary amine.

High-performance liquid chromatography (HPLC), is a technique inanalytical chemistry used to separate, identify, and quantify eachcomponent in a mixture. For a review of HPLC, see A. M. Sabir et al.,Int. Res. J. Pharm., 2013, 4, 4, 39-46.

Solvents referred to herein include MeCN (acetonitrile), DCM(dichloromethane), acetone, IPA (isopropyl alcohol), iPrOAc (isopropylacetate), TBME (t-butyl methyl ether), THF (tetrahydrofuran), 2-MeTHF(2-methyl tetrahydrofuran), EtOAc (ethyl acetate), ethanol and toluene.As used herein, the term ether solvent means a solvent containing analkyl-O-alkyl moiety, wherein the two alkyl components may be connected.Ether solvents include diethyl ether, TBME, THF and 2-MeTHF.

A drying agent is a chemical used to remove water from an organiccompound that is in solution. Examples of drying agents include calciumchloride, magnesium sulphate, and sodium sulphate. Drying agentsdescribed herein are typically magnesium sulphate.

An acidic reagent suitable for crystallising a pharmaceuticallyacceptable salt of a compound of formula (I) (or (I′)) is an acid whichforms a non-toxic acid anion. Examples include hydrochloride,hydrobromide, sulphate, phosphate or acid phosphate, acetate, maleate,fumarate, lactate, tartrate, citrate and gluconate.

Aqueous basic solution means a mild base suitable for workup, forexample a 10% potassium carbonate solution.

As described above, Scheme 2 depicts advantageous methods ofsynthesising compounds of formula (I) (or (I′)), or a pharmaceuticallyacceptable salts thereof, comprising Stage 1 and Stage 2. Stage 1comprises:

-   -   (i) reacting a starting carboxylic acid (auxin or a derivative        thereof) with two or more coupling agents to produce an        activated compound; and    -   (ii) reacting the activated compound with an amine having the        formula (R²)(R³)NH to produce a compound of formula (II).

The activated compound is the product of the reaction between the auxinstarting material and the two or more coupling agents. Where the two ormore coupling agents comprise carboxylic acid activating agents, theactivated compound comprises an activated moiety, derived from theoriginal carboxylic acid moiety, which is more likely to react with anamine than the original carboxylic acid moiety.

In some embodiments, the two or more coupling agents comprise acarboxylic acid activating agent. In some embodiments, the two or morecoupling agents comprise an additive coupling agent. In someembodiments, the additive is capable of reacting with the product of thereaction of the starting carboxylic acid and the coupling agent (theproduct being a compound comprising an activated moiety) to produce anactivated compound comprising an even more activated moiety that is morelikely to react with an amine than the original activated moiety.

Often, the two or more coupling agents comprise a carboxylic acidactivating agent and an additive coupling agent.

In some embodiments, at least one of the two or more coupling agents isselected from the group consisting of carbodiimide coupling agents,phosphonium coupling agents and3-(diethoxy-phosphoryloxy)-1,2,3-benzo[d]triazin-4(3H)-one (DEPBT), suchas a carbodiimide coupling agent or a phosphonium coupling agent. Insome embodiments, at least one of the two or more coupling agents is acarbodiimide coupling agent.

A carbodiimide coupling agent is a coupling agent which comprises acarbodiimide group R′—N═C═N—R″, wherein R′ and R″ are hydrocarbyl groupsoptionally substituted with heteroatoms selected from nitrogen, sulfurand oxygen, typically nitrogen. Often, R′ and R″ are independentlyselected from C₁-C₆alkyl, C₅-C₆cycloalkyl, C₁-C₆alkylamino andmorpholinoC₁-C₆alkyl. Often, C₁-C₆alkyl is C₃alkyl, C₅-C₆cycloalkyl iscyclohexyl, C₁-C₆alkylamino is dimethylaminopropyl and/ormorpholinoC₁-C₆alkyl is morpholinoethyl.

In some embodiments, the carbodiimide coupling agent is any one selectedfrom the group consisting of dicyclohexylcarbodiimide (DCC),diisopropylcarbodiimide (DIC),(N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and1-cyclohexyl-(2-morpholinoethyl)carbodiimide metho-p-toluene sulfonate(CMCT). In some embodiments, the carbodiimide coupling agent is any oneselected from the group consisting of dicyclohexylcarbodiimide (DCC),diisopropylcarbodiimide (DIC) and(N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC). Often, thecarbodiimide coupling agent isN-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC), typically as ahydrochloride salt (EDC·HCl). EDC or EDC·HCl are particularly preferredas they are non-toxic and are highly water soluble, facilitating theirvirtually complete removal in workup and wash steps of Stage 1.

A phosphonium coupling agent comprises a phosphonium cation and acounterion, typically a hexafluorophosphate anion. In some embodiments,the phosphonium cation is of formula [PR^(a) ₃R^(b)]⁺ wherein R^(a) isdi(C₁-C₆)alkylamino or pyrrolidinyl and R^(b) is halo or a hydrocarbylgroup optionally substituted with nitrogen and/or oxygen atoms. Often,R^(b) is bromo, benzotriazol-1-yloxy or 7-aza-benzotriazol-1-yloxy.

In some embodiments, the phosphonium coupling agent is any one selectedfrom the group consisting ofbenzotriazol-1-yloxy-tris(dimethylamino)-phosphonium hexafluorophosphate(BOP), bromo-tripyrrolidino-phosphonium hexafluorophosphate (PyBrOP),benzotriazol-1-yloxy-tripyrrolidino-phosphonium hexafluorophosphate(PyBOP), 7-aza-benzotriazol-1-yloxy-tripyrrolidinophosphoniumhexafluorophosphate (PyAOP) and ethyl cyano(hydroxyimino)acetato-O₂)tri-(1-pyrrolidinyl)-phosphonium hexafluorophosphate (PyOxim).

In some embodiments, at least one of the two or more coupling agents isan additive coupling agent selected from the group consisting of1-hydroxybenzotriazole (HOBt),hydroxy-3,4-dihydro-4-oxo-1,2,3-benzotriazine (HOOBt),N-hydroxysuccinimide (HOSu), 1-hydroxy-7-azabenzotriazole (HOAt), ethyl2-cyano-2-(hydroximino)acetate (Oxyma Pure),4-(N,N-Dimethylamino)pyridine (DMAP),N-hydroxy-5-norbornene-2,3-dicarboximide (HONB),6-chloro-1-hydroxybenzotriazole (6-Cl-HOBt),3-hydroxy-4-oxo-3,4-dihydro-1,2,3-benzotriazine (HODhbt),3-hydroxy-4-oxo-3,4-dihydro-5-azabenzo-1,2,3-triazene (HODhat) and3-hydroxyl-4-oxo-3,4-dihydro-5-azepine benzo-1,3-diazines (HODhad).

In some embodiments, at least one of the two or more coupling agents isan additive coupling agent selected from the group consisting of1-hydroxybenzotriazole (HOBt),hydroxy-3,4-dihydro-4-oxo-1,2,3-benzotriazine (HOOBt),N-hydroxysuccinimide (HOSu), 1-hydroxy-7-azabenzotriazole (HOAt), ethyl2-cyano-2-(hydroximino)acetate (Oxyma Pure) and4-(N,N-Dimethylamino)pyridine (DMAP).

In some embodiments, at least one of the two or more coupling agents isan additive coupling agent which is 1-hydroxybenzotriazole.

In some embodiments, the two or more coupling agents consist of acoupling agent and an additive coupling agent wherein the coupling agentand additive coupling agent may be as described in the aboveembodiments.

A benefit of using both a coupling agent and an additive coupling agentis an increased rate of formation of the Stage 1 product from thestarting material and an amine having the formula (R²)(R³)NH. Inaddition, when an additive coupling agent is used together with acarbodiimide coupling agent, the likelihood of unwanted side reactionsmay be reduced. For example, reaction of a starting carboxylic acid witha carbodiimide coupling reagent is likely to form an O-acylisourea. Thismay undergo a rearrangement to form an N-acylurea, which is a stablecompound unlikely to react with an amine. Additive coupling reagents mayreact with O-acylureas before rearrangement to N-acylureas, and producecompounds that go on to react with an amine, rather than inactiveN-acylureas.

Therefore, in some embodiments, the two or more coupling agents consistof a carbodiimide coupling agent and an additive coupling agent.

In particular embodiments, the two or more coupling agents consist ofN-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC), typically as ahydrochloride salt (EDC·HCl), and 1-hydroxybenzotriazole (HOBt).

Often, an excess of coupling agent with respect to start a carboxylicacid is used. In some embodiments, the ratio of coupling agent:startingcarboxylic acid is about 1:1 to about 3:1, typically about 1:1 to about2:1 and most typically about 1:1 to about 1.5:1.

Often, an excess of additive coupling agent with respect to startingcarboxylic acid is used. In some embodiments, the ratio of additivecoupling agent:starting carboxylic acid is about 1:1 to about 3:1,typically about 1:1 to about 2:1 and most typically about 1:1 to about1.5:1.

In some embodiments, where the two or more coupling agents comprise acoupling agent and an additive coupling agent, a ratio of couplingagent:starting carboxylic acid and additive coupling agent:startingcarboxylic acid of about 1:1 to about 1.5:1 is used.

As described above, Stage 1 of Scheme 2 comprises reacting the activatedcompound (the product of reacting a starting carboxylic acid, forexample of formula (III)) with two or more coupling agents) with anamine having the formula (R²)(R³)NH to produce the product of Stage 1.

The ratio of amine:starting carboxylic acid employed in the method isoften about ≥1:1. In some embodiments, the ratio of amine:startingcarboxylic acid is about 1:1 to about 3:1, typically about 1:1 to about2:1.

In some embodiments, Stage 1 further comprises isolating the resultantcompound (the amide of formula (II)). The skilled person is aware oftechniques in the art suitable for isolation of such compounds forexample, such amides may be extracted into an organic solvent such asdichloromethane or ethyl acetate, washed with an aqueous solution suchas an aqueous basic solution, and concentrated. To increase purity, theisolated amide may be recrystallized. The skilled person is aware oftechniques that are suitable for doing this for example, the amide maybe dissolved in the minimum amount of solvent at a particulartemperature (e.g. at ambient temperature (e.g. about 15 to about 25° C.)or at elevated temperatures where heat is applied to the solution) andthe resultant solution cooled to encourage precipitation. Alternatively,or additionally, the volume of the solution may be reduced to encourageprecipitation, e.g. by simple evaporation at ambient temperature andpressure. Alternatively, or in addition, an anti-solvent may be used (inwhich the amide is less soluble than the solvent already present).

Isolated amides are stable and may be stored as solids at ambienttemperature, e.g. at about 15 to about 25° C., in the air. They may, butneed not be, stored under inert conditions, e.g. under nitrogen orargon, or at reduced temperatures, e.g. in a refrigerator or freezer.

Typically, steps (1) and (2) of Stage 1 of Scheme 2 (for example, butnot necessarily (1) CH₂Cl₂/HOBt/EDC and (2) 2 M N(H)R²R³ in THF (theillustrative conditions mentioned in the legend to Scheme 2 above) arecarried out in a suitable solvent. The skilled person is able to assesswhich solvents are suitable for these steps. Examples of suitablesolvents include dichloromethane (DCM), acetone, isopropyl alcohol(IPA), isopropyl acetate (iPrOAc), tert-butyl methyl ether (TBME),2-methyl tetrahydrofuran (2-MeTHF) and ethyl acetate (EtOAc). In someembodiments, steps (1) and (2) of Stage 1 are carried out indichloromethane.

Steps (1) and (2) of Stage 1 are carried out at a suitable temperatureand the skilled person is able to assess which temperatures are suitablefor these steps. Often, steps (1) and (2) of Stage 1 are carried out attemperatures of about 10° C. to about 30° C. In some embodiments, steps(1) and (2) of Stage 1 are carried out at room temperature (e.g. atabout 20 to about 30° C. (typically about 20° C.)).

In specific embodiments, Stage 1 of the method depicted in Scheme 2, andthus in particular embodiments of the seventh aspect of the invention(involving reaction of compounds of formula (III)) comprises the stepsof:

-   -   (1) contacting a starting carboxylic acid of formula (III) and        between 1 and 1.5 equivalents of an additive coupling agent, and        between 1 and 1.5 equivalents of a carbodiimide coupling agent        to produce a first composition; and    -   (2) contacting the first composition with between 1 and 2        equivalents of an amine having the formula R²R³NH or R²R³ND to        produce a second composition.

In some embodiments, 1 g or more, such as 1 g to 100 kg or 1 g to 1 kgof a starting compound (the carboxylic acid) is employed in the methodof the invention.

In some embodiments, the contacting of steps (1) and (2) is carried outin the presence of a first solvent, such as between 5 and 20 volumes ofa first solvent. The first solvent may be selected from any one ofdichloromethane (DCM), acetone, isopropyl alcohol (IPA), isopropylacetate (iPrOAc), tert-butyl methyl ether (TBME), 2-methyltetrahydrofuran (2-MeTHF) and ethyl acetate (EtOAc). Typically, thefirst solvent is DCM.

In some embodiments, step (1) further comprises stirring or agitatingthe first composition. The first composition may be stirred or agitatedfor at least 30 minutes, such as 30 minutes to 3 hours or 30 minutes to2 hours, preferably at least 1 hour, for example 1 to 3 hours or 1 to 2hours. The first composition may be maintained at a temperature ofbetween 10° C. and 30° C.

In some embodiments, the amine of step (2) is dissolved in a solvent,such as tetrahydrofuran (THF) or ether, prior to contacting. The aminemay be present in the solvent at a concentration of about 2 M.Typically, the amine of step (2) is dissolved in THF.

In some embodiments, step (2) further comprises stirring or agitatingthe second composition. The second composition may be stirred oragitated for at least 30 minutes, such as 30 minutes to 3 hours or 30minutes to 2 hours, preferably at least 1 hour, for example 1 to 3 hoursor 1 to 2 hours. The second composition may be maintained at atemperature of between 10° C. and 30° C.

In some embodiments, step (2) further comprises contacting the secondcomposition with an aqueous basic solution to produce a thirdcomposition, for example contacting the second composition with between2 and 10 volumes of an aqueous basic solution such as an aqueoussolution comprising potassium carbonate.

In some embodiments, step (2) further comprises stirring or agitatingthe third composition. The third composition may be stirred or agitatedfor at least 1 minute, such as 1 to 15 minutes or 1 to 10 minutes,preferably at least 5 minutes, for example 5 to 15 minutes or 5 to 10minutes. The third composition may be maintained at a temperature ofbetween 10° C. and 30° C.

In some embodiments, where the third composition comprises an organicand an aqueous component, step (2) further comprises separating theorganic component from the aqueous component. In some embodiment, theorganic component is separated from the aqueous component within 8 hoursof the contacting of step (1).

In even more specific embodiments, Stage 1 in methods of the seventhaspect of the invention comprises the steps of:

-   -   i. adding to a first vessel 1 g or more of a starting carboxylic        acid of formula (III) and between 1 and 1.5 equivalents of an        additive coupling agent,    -   ii. adding to the first vessel between 5 and 20 volumes of a        first solvent selected from DCM, acetone, IPA, iPrOAc, TBME,        2-MeTHF and EtOAc,    -   iii. adding to the first vessel between 1 and 1.5 equivalents of        a carbodiimide coupling agent,    -   iv. stirring the contents of the first vessel for at least 30        minutes, preferably at least 1 hour (such as 1 to 2 hours), at        between 10° C. and 30° C.,    -   v. adding to the first vessel between 1 and 2 equivalents of an        amine having the formula R²R³NH or R²R³ND, wherein the amine is        preferably dissolved in an ether solvent,    -   vi. further stirring the contents of the first vessel for at        least 30 minutes, preferably at least 1 hour (such as 1 to 2        hours), at between 10° C. and 30° C.,    -   vii. adding to the first vessel between 2 and 10 volumes of an        aqueous basic solution,    -   viii. further stirring the contents of the first vessel for at        least 1 minute, preferably at least 5 minutes (such as 5 to 10        minutes), at between 10° C. and 30° C.,    -   ix. allowing an immiscible organic fraction to separate from an        aqueous fraction, wherein the organic fraction comprises the        amide product of Stage 1, and    -   x. removing the organic fraction comprising the amide product,        wherein steps i. to x. are carried out within a single 8 hour        period.

In some embodiments, the first solvent is DCM.

In some embodiments, the amine is dimethylamine. In some embodiments,the amine is dissolved in THF, for example at a concentration of 2 M.

In some embodiments, the aqueous basic solution comprises potassiumcarbonate.

In even more specific embodiments, Stage 1 of the method of Scheme 2further comprises the steps of:

-   -   xi. drying the organic fraction with a drying agent, for example        a drying agent selected from calcium chloride, magnesium        sulphate, and sodium sulphate,    -   xii. filtering the organic fraction,    -   xiii. concentrating the organic fraction, for example under        vacuum such as under a pressure of less than 1 atmosphere,    -   xiv. adding the concentrated organic fraction to a second        vessel,    -   xv. adding between 2 and 10 volumes of a second solvent to the        second vessel, wherein the second solvent is selected from IPA,        EtOAc, IPrOAc, acetonitrile (MeCN), TBME, THF, 2-MeTHF and        toluene,    -   xvi. stirring the contents of the second vessel for at least 1        hour, preferably at least 2 hours (such as 2 to 3 hours), at        temperatures of between 45° C. and 55° C.,    -   xvii. cooling the contents of the second vessel to temperatures        of between 15° C. and 25° C.,    -   xviii. filtering contents of the second vessel to obtain a        filtrate, wherein the filtrate comprises the amide product of        Stage 1, and    -   xix. drying the filtrate.

In some embodiments, the drying agent of step xi. is magnesium sulphate.In some embodiments, the solvent of step xv. is selected from TBME andIPA.

Stage 2 of the method of Scheme 2 comprises reacting the amide productof Stage 1 (the compound of formula (II)) with LiAlH₄ and/or LiAlD₄ toproduce a compound of formula (I′). Optionally, as described above, itmay be desired to convert certain compounds of formula (I′) to compoundsof formula (I) as described herein.

As described above, LiAlH₄, LiAlD₄ or mixtures of the two may be reactedwith the amide. In preferred embodiments, Stage 2 of the methodcomprises reacting the amide with a mixture of LiAlH₄ and LiAlD₄. Suchmixtures may comprise LiAlD₄ and comprise between 0.1 and 99.9% hydride.Mixtures of between 2% and 98% lithium aluminium hydride or between 2%and 98% lithium aluminium deuteride may be employed. Sometimes, mixturesof LiAlH₄ and LiAlD₄ consist essentially of 98% LiAlD₄/2% LiAlH₄.Sometimes, such mixtures consist essentially of 95% LiAlD₄/5% LiAlH₄,95% LiAlD₄/5% LiAlH₄, 85% LiAlD₄/15% LiAlH₄, 80% LiAlD₄/20% LiAlH₄, 75%LiAlD₄/25% LiAlH₄, 70% LiAlD₄/30% LiAlH₄, 65% LiAlD₄/35% LiAlH₄, 60%LiAlD₄/40% LiAlH₄, 55% LiAlD₄/45% LiAlH₄, 50% LiAlD₄/50% LiAlH₄, 45%LiAlD₄/55% LiAlH₄, 40% LiAlD₄/60% LiAlH₄, 35% LiAlD₄/65% LiAlH₄, 30%LiAlD₄/70% LiAlH₄, 25% LiAlD₄/75% LiAlH₄, 20% LiAlD₄/80% LiAlH₄, 15%LiAlD₄/85% LiAlH₄, 10% LiAlD₄/90% LiAlH₄, 5% LiAlD₄/95% LiAlH₄, or 2%LiAlD₄/98% LiAlH₄.

By the mixtures of LiAlH₄ and LiAlD₄ consisting essentially of specifiedpercentages of LiAlH₄ and LiAlD₄ is meant that the mixture may compriseadditional components (other than LiAlH₄ and LiAlD₄) but that thepresence of these additional components will not materially affect theessential characteristics of the mixture. In particular, mixturesconsisting essentially of LiAlH₄ and LiAlD₄ will not comprise materialamounts of agents that are detrimental to the reduction of amides toproduce compounds of formula (I′) (e.g. material amounts of agents thatreact with LiAlH₄ and LiAlD₄, the amide reactant and/or compounds offormula (I′) in a way that inhibits the reduction of the carbonyl moietyof the amides of formula (II) to produce compounds of formula (I′).

The amount of LiAlH₄ or LiAlD₄ comprised in mixtures of the two dependson the degree of α-deuteration sought in the compound of formula (I′)(and (I)). For example, where compounds of formula (I(′)) are sought inwhich one ^(y)H is protium and the other is deuterium, a mixture of 50%LiAlH₄ and 50% LiAlD₄ may be preferred. Alternatively, where a mixtureof compounds of formula (I′)) is sought, in which approximately half ofthe compounds comprise two deuterium atoms at the α-position (i.e. both^(x)H are deuterium) and approximately half of the compounds compriseone deuterium atom and one protium atom at the α-position (i.e. one^(y)H is deuterium and the other is protium), a mixture of 25% LiAlH₄and 75% LiAlD₄ may be preferred.

The amount of LiAlH₄ and/or LiAlD₄ employed relative to the amide beingreduced in Stage 2 of Scheme 2 is often ≤1:1. For the avoidance ofdoubt, the ratios of LiAlH₄ and/or LiAlD₄ relative to the amide refer tothe total amount of LiAlH₄ and/or LiAlD₄ used with respect to the amideof formula (II). In some embodiments, the ratio of LiAlH₄ and/orLiAlD₄:compound of formula (II) is 0.5:1 to 1:1, such as 0.8:1 to 1:1.In some embodiments, the ratio of LiAlH₄ and/or LiAlD₄:compound offormula (II) is 0.9:1.

Typically, Stage 2 of Scheme 2 is carried out in a suitable solvent. Theskilled person is able to assess which solvents are suitable for this.Examples of suitable solvents include ethers such as THF and diethylether. In some embodiments, Stage 2 is carried out in THF.

In some embodiments, the LiAlH₄ and/or LiAlD₄ is provided as a solutionor suspension of LiAlH₄ and/or LiAlD₄ in a suitable solvent such as anether, for example THF or diethyl ether, typically THF.

Stage 2 of Scheme 2 is carried out at a suitable temperature and theskilled person is able to assess which temperatures are suitable forthese steps. Often, Stage 2 of Scheme 2 is carried out at temperaturesof about −5° C. to about 65° C.

In some embodiments, Stage 2 of scheme 2 further comprises isolating thecompound or compounds resultant from the reduction the skilled person isaware of techniques in the art suitable for doing this for example, onquenching the reaction (e.g. with an aqueous solution of a tartrate saltsuch as Rochelle's salts), the product resultant from Stage 3 of Scheme2 may be extracted into an organic solvent such as an ether, e.g. THF ordiethyl ether, washed with an aqueous solution such as an aqueous basicsolution, and concentrated. The isolated compound from Stage 2 of Scheme2 may be recrystallized. The skilled person is aware of techniques thatare suitable for such recrystallisations. Examples of recrystallisationtechniques described with respect to recrystallisation of compoundsresultant from Stage 2 of Scheme 2 apply mutatis mutandis torecrystallisation of salts of these compounds (resultant from Stage 3).

In some embodiments, about 1 g or more, such as about 1 g to about 100kg or about 1 g to about 1 kg of a compound resultant from Stage 2 ofScheme 2 is employed.

In specific embodiments, Stage 2 of Scheme 2 comprises contacting acompound resultant from Stage 1 (i.e. a compound of formula (II)) andbetween about 0.8 and about 1 equivalents, such as about 0.9 equivalentsof LiAlH₄ and/or LiAlD₄ to produce a first composition.

In some embodiments, the contacting is carried out in the presence of asolvent such as an ether, e.g. THF or diethyl ether, typically THF.

In some embodiments, the contacting comprises dropwise addition ofLiAlH₄ and/or LiAlD₄ to an amide, wherein LiAlH₄ and/or LiAlD₄ isprovided as a solution or suspension of LiAlH₄ and/or LiAlD₄ in asuitable solvent, such as an ether, e.g. THF or diethyl ether. In someembodiments, LiAlH₄ and/or LiAlD₄ is provided as a 2.4 M or 2 M solutionor suspension of LiAlH₄ and/or LiAlD₄ in THF. In some embodiments, theLiAlH₄ and/or LiAlD₄ is provided as a 2 M solution or suspension ofLiAlH₄ and/or LiAlD₄ in THF.

In some embodiments, the contacting is carried out at temperatures ofabout −5° C. to about 65° C.

In some embodiments, Stage 2 further comprises stirring or agitating thefirst composition. The first composition may be stirred or agitated forabout 1 hour to about 6 hours, typically for about 2 hours. The firstcomposition may be stirred or agitated at a temperature of about 55° C.to about 65° C. In some embodiments, the first composition is stirred oragitated at a temperature of about 55° C. to about 65° C. and thencooled to temperatures of about 10° C. to about 30° C.

In some embodiments, the amide is contacted with about 0.9 equivalentsof LiAlH₄ and/or LiAlD₄.

In specific embodiments, Stage 2 of Scheme 2 comprises the steps of:

-   -   i. adding to a third vessel 1 g or more (such as 1 g to 1 kg) of        an amide to be reduced,    -   ii. adding to the third vessel between 5 and 20 volumes of an        ether solvent,    -   iii. adding to the third vessel, dropwise over at least 15        minutes (e.g. 15 to 30 minutes), a solution of between 0.8 and 1        equivalents of LiAlH₄ and/or LiAlD₄ in the ether solvent at a        temperature of between −5° C. and 65° C.,    -   iv. stirring the contents of the third vessel at between 55° C.        and 65° C. for between 1 hour and 6 hours, preferably 2 hours,        and    -   v. cooling the contents of the third vessel to between 10° C.        and 30° C.,        wherein the contents of the third vessel comprise a compound of        formula (I′)

In some embodiments, the ether solvent is THF. In some embodiments, 0.9equivalents of LiAlH₄ and/or LiAlD₄ are added to the third vessel instep iii. The LiAlH₄ and/or LiAlD₄ is typically added to the thirdvessel as a 2.4 M or 2 M solution in THF. In some embodiments, theLiAlH₄ and/or LiAlD₄ is added to the third vessel as a 2 M solution inTHF.

In even more specific embodiments, Stage 2 of Scheme 2 comprises aworkup comprising the steps of:

-   -   vi. adding between 5 and 20 volumes of an aqueous solution of a        tartrate salt (such as Rochelle's salts) to a fourth vessel,    -   vii. adding a composition comprising crude compound of formula        (I), over at least 15 minutes (such as 15 minutes to 1 hour),        preferably at least 30 minutes (such as 30 minutes to 1 hour),        to the fourth vessel at between 15° C. and 25° C., and    -   viii. stirring the contents of the fourth vessel at between        15° C. and 25° C. for at least 30 minutes (such as 30 minutes to        1 hour).

For the avoidance of doubt, the composition comprising crude compound offormula (I′) refers to the contents of the third vessel on completion ofstep v. of Stage 2, described above.

In further specific embodiments, Stage 2 of Scheme 2 further comprisesthe steps of:

-   -   ix. allowing an organic fraction to separate from an aqueous        fraction, wherein the organic fraction comprises the compound of        formula (I′),    -   x. removing the aqueous fraction from the fourth vessel,    -   xi. adding between 5 and 20 volumes of a brine solution to the        fourth vessel,    -   xii. stirring the contents of the fourth vessel at a temperature        between 15° C. and 25° C. for at least 5 minutes (such as 5 to        15 minutes),    -   xiii. removing the organic fraction comprising the compound of        formula (I′) as a freebase,    -   xiv. drying the organic fraction using a drying agent, such as a        drying agent selected from calcium chloride, magnesium sulphate,        and sodium sulphate,    -   xv. filtering the organic fraction, and    -   xvi. concentrating the organic fraction, for example under        vacuum such as under a pressure of less than 1 atmosphere.

Isolated compounds of formula (I′) (produced via Stage 2) are stable andmay be stored as solids at ambient temperature, e.g. at about 20° C., inthe air. They may, but need not be, stored under inert conditions, e.g.under nitrogen or argon, or at reduced temperatures, e.g. in arefrigerator or freezer. In some embodiments, the compound of formula(I) is stored in a solvent, for example dissolved in ethanol. In someembodiments, the compound of formula (I′) is stored in a solvent formore than 8 hours, typically more than 12 hours.

As described above, the method of Scheme 2 provides a method of orcomprising synthesising a compound of formula (I′), or apharmaceutically acceptable salt thereof. In some embodiments, theinvention provides a method of or comprising synthesising apharmaceutically acceptable salt of formula (I′). A pharmaceuticallyacceptable salt may be formed from a compound of formula (I′) byreaction with a suitable acid. Thus, in some optional embodiments, themethod of Scheme 2 comprises Stage 3 (as is depicted in Scheme 2), inwhich the compound of formula (I′) is reacted with an acidic reagent toproduce a pharmaceutically acceptable salt of the compound of formula(I′) in some embodiments, the acidic reagent is suitable forcrystallising a pharmaceutically acceptable salt of the compound offormula (I′). It will be understood that, in embodiments in whichcompounds of formula (I′) comprise a moiety of formula OPR, theprotecting group PR will typically be removed and the resultant hydroxylgroup optionally manipulated as described herein prior to Stage 3(formation of pharmaceutically acceptable salts).

Thus, in some embodiments, the invention provides a method ofsynthesising a compound of formula (I) or (I′), or a pharmaceuticallyacceptable salt thereof, comprising Stage 1, Stage 2 and Stage 3,wherein Stage 1 comprises:

-   -   (i) reacting a carboxylic acid (for example of formula (III))        with two or more coupling agents to produce an activated        compound;    -   (ii) reacting the activated compound with an amine having the        formula R²R³NH or R²R³ND to produce an amide (for example of        formula (II); and    -   (iii) isolating the amide;    -   Stage 2 comprises reacting the amide with LiAlH₄ and/or LiAlD₄;        and    -   Stage 3 comprises the step of reacting the compound (for example        of (I) or (I′)) with an acidic reagent suitable for        crystallising a pharmaceutically acceptable salt of the compound        of formula (I) or (I′).

In some embodiments, a ratio of acidic reagent:compound of formula (I)or (I′) of ≥1:1 is used. Often, the ratio of acidic reagent:compound offormula (I(′)) is 1:1.

Typically, Stage 3 of the method is carried out in a suitable solvent.The skilled person is able to assess which solvents are suitable forStage 3. Examples of suitable solvents include ethanol, IPA, iPrOAc andMeCN. In some embodiments, Stage 3 is carried out in ethanol.

Stage 3 of the method of the invention is carried out at a suitabletemperature and the skilled person is able to assess which temperaturesare suitable for these steps.

In some embodiments, Stage 3 of the method comprises contacting acompound of formula (I) (or (I′) and an acidic reagent to produce afirst composition. Often, the contacting of Stage 3 is carried out attemperatures of 70 to 100° C., for example 70 to 90° C. or 70 to 80° C.In some embodiments, the contacting of Stage 3 is carried out attemperatures of about 75° C.

In some embodiments, Stage 3 further comprises isolating thepharmaceutically acceptable salt of formula (I) or (I′). The skilledperson is aware of techniques in the art suitable for isolation of sucha compound. For example, where the compound is dissolved within asuspension, it may be separated from some of the other components of thesuspension via filtration, such as hot filtration. The pharmaceuticallyacceptable salt of formula (I) or (I′) may precipitate from thefiltrate. The skilled person is aware of methods to encourageprecipitation of a compound from a solution, such as cooling thesolution, concentrating the solution and/or adding into the solution acrystalline form of the compound to encourage nucleation and the growthof further crystals of the compound from the solution (i.e. seeding).The pharmaceutically acceptable salt of formula (I) or (I′) may berecrystallized. The skilled person is aware of techniques that aresuitable for recrystallisation of a pharmaceutically acceptable salt offormula (I) or (I′) the examples of recrystallisation techniquesdescribed with respect to recrystallisation of the inmates resultantfrom Stage 2 apply mutatis mutandis to recrystallisation of apharmaceutically acceptable salt of formula (I) or (I′).

In more specific embodiments, Stage 3 of the method of the inventioncomprises the steps of:

-   -   i. adding to a fifth vessel at least one equivalent of an acidic        reagent suitable for crystallising a pharmaceutically acceptable        salt of a compound of formula (I) or (I′),    -   ii. dissolving a compound of formula (I) or (I′) as a freebase        in between 5 and 20 volumes of a solvent such as a solvent        selected from ethanol, IPA, iPrOAc and MeCN and adding the        solution to the fifth reaction vessel,    -   iii. stirring the contents of the fifth vessel at a temperature        of above 72° C. (such as 72 to 90° C.),    -   iv. filtering the contents of the fifth vessel,    -   v. adding the filtrate to a sixth vessel and cooling the        contents to a temperature of 67° C. to 73° C.,    -   vi. optionally seeding the sixth vessel with a crystalline form        of the pharmaceutically acceptable salt of the compound of        formula (I) or (I′),    -   vii. stirring the contents of the sixth vessel at a temperature        of 67° C. to 73° C. for at least 30 minutes (such as 30 minutes        to 1 hour),    -   viii. cooling the contents of the sixth vessel to a temperature        of −5° C. to 5° C. at a rate of 2 to 8° C. per hour, and    -   ix. filtering the contents of the sixth vessel to produce a        filter cake comprising a pharmaceutically acceptable salt of the        compound of formula (I) or (I′).

In some embodiments, the solvent of step ii. is ethanol. In someembodiments, the rate of cooling in step viii. is 5° C. per hour.

P. H. Stahl and C. G. Wermuth provide an overview of pharmaceuticalsalts and the acids comprised therein in Handbook of PharmaceuticalSalts: Properties, Selection and Use, Weinheim/Zürich: Wiley-VCH/VHCA,2002. The acids described in this review are suitable acidic reagents inorder to provide pharmaceutically acceptable salts of or for use inaccordance with the various aspects of the present invention.

In some embodiments, the acidic reagent is any one selected from thegroup consisting of fumaric acid, tartaric acid, citric acid,hydrochloric acid, acetic acid, lactic acid, gluconic acid,1-hydroxy-2-naphthoic acid, 2,2-dichloroacetic acid,2-hydroxyethanesulfonic acid, 2-oxoglutaric acid, 4-acetamidobenzoicacid, 4-aminosalicylic acid, adipic acid, ascorbic acid, aspartic acid,benzenesulfonic acid, benzoic acid, camphoric acid, camphor-10-sulfonicacid, decanoic acid, hexanoic acid, octanoic acid, carbonic acid,cinnamic acid, cyclamic acid, dodecylsulfuric acid,ethane-1,2-disulfonic acid, ethanesulfonic acid, formic acid, galactaricacid, gentisic acid, glucoheptonic acid, glucuronic acid, glutamic acid,glutaric acid, glycerophosphoric acid, glycolic acid, hippuric acid,hydrobromic acid, isobutyric acid, lactobionic acid, lauric acid, maleicacid, malic acid, malonic acid, mandelic acid, methanesulfonic acid,naphthalene-1,5-disulfonic acid, naphthalene-2-sulfonic acid, nicotinicacid, nitric acid, oleic acid, oxalic acid, palmitic acid, pamoic acid,phosphoric acid, proprionic acid, pyroglutamic acid (—L), salicylicacid, sebacic acid, stearic acid, succinic acid, sulfuric acid,thiocyanic acid, toluenesulfonic acid and undecylenic acid.

Often, the acidic reagent is any one selected from fumaric acid,tartaric acid, citric acid and hydrochloric acid. In particularembodiments, the acidic reagent is fumaric acid.

The amides resultant from Stage 2 are produced on reacting a startingcarboxylic acid with two or more coupling agents to produce an activatedcompound, and reacting the activated compound with an amine having theformula R²R³NH or R²R³ND. For the avoidance of doubt, the R² and R³groups of the amides resultant from Stage 1 and compounds of formula (I)or (I′) resultant from Stage 2 (and Stage 3) are derived from the R² andR³ groups of the amine of formula R²R³NH.

The compound of formula (I′) is produced on reacting the compound offormula (II) with LiAlH₄ and/or LiAlD₄. Without wishing to be bound bytheory, the hydride or deuteride ions provided by LiAlH₄ and/or LiAlD₄bind to the carbon atom of the carbonyl of formula (II), resulting inthe formation of the compound of formula (I′). For the avoidance ofdoubt, the ^(y)H groups in formulae ((I) and (I′) are derived from thehydride or deuteride ions provided by LiAlH₄ and/or LiAlD₄.

In some embodiments, at least one ^(y)H is deuterium, i.e. the compoundof formula (I′) is produced on reacting the compound of formula (II)with LiAlD₄ or a mixture of LiAlD₄ and LiAlH₄.

The method of the seventh aspect of the present invention isparticularly useful in allowing access to therapeutically usefulα-deuterated compounds (i.e. in which there is a greater than naturalpreponderance of deuterium at the alpha position in addition to in amethyl group (R² and/or R³), as the method employs significantly lessLiAlD₄ than related syntheses known in the art as the method substitutesdeuterium at the alpha position but not the beta position. LiAlD₄ isamong the most expensive and difficult to manufacture reagents in thissynthesis. Moreover, optimised methods of the present invention reduceLiAlH₄ and/or LiAlD₄ requirements, for example from 2 equivalents to 0.9equivalents which increases economic efficiency in manufacturingdeuterated compounds of formula (I) and or (I′). In view of this,compounds of formula (I′) and (I′) are cheaper to make, via the methodsof the present invention, than other related deuterated compounds, whichare typically deuterated at both the alpha and beta position.

As described above, the method of the seventh aspect invention issuitable for the production of high purity compounds of formula (I) and(I′). In some embodiments, the compound of formula (I) or (I′), or apharmaceutically acceptable salt thereof, is produced at a purity ofbetween 99% and 100% by HPLC, such as a purity of between 99.5% and 100%by HPLC. In some embodiments, the compound of formula (I) or (I′), or apharmaceutically acceptable salt thereof, is produced at a purity ofbetween 99.9% and 100% by HPLC, such as a purity of between 99.95% and100% by HPLC.

The chemistry described in connection with the seventh aspect of theinvention and Scheme 2 details chemistry that may be practised tosynthesise, efficiently, pre-GMP and GMP batches of DMT-based drugsubstances, including compounds of formula (I). In particular, thecoupling agents HOBt and EDC·HCl. may be employed to increase the yieldof step 1 from less than 70% to greater than 90%. This enables efficientscaling of drug substance batches under GMP standards with overall yieldof 65% and above.

A series of DMT-based drug substances, each selectively enriched withdeuterium in a GMP-compatible route, some in accordance with formula (I)and others nevertheless of use in the present invention (for instance inits third aspect), were prepared using modified versions of Scheme 2 asfollows (with the labelling with reference to formula (I):

R², R³ C(^(y)H)₂ Mwt Modification(s) to Scheme 2* (CH₃)₂ CH₂ 188.3 None(CH₃)₂ C(H)D 189.3 Stage 2.1:1:1 LiAlH₄:LiAlD₄ (0.9 equivalents of each)in THF (CH₃)₂ CD₂ 190.3 Stage 2.1: LiAlD₄ (0.9 equivalents) in THF(CD₃)₂ CH₂ 194.3 Step 1.3: ND(CD₃)₂ . . . DCI (1.5 equivalents) withDIPEA (4 equivalents) (CD₃)₂ C(H)D 195.3 Stage 1.3: ND(CD₃)₂ . . . DCI(1.5 equivalents) with DIPEA (4 equivalents) Step 2.1:1:1 LiAlH₄:LiAlD₄(0.9 equivalents of each) in THF (CD₃)₂ CD₂ 196.3 Stage 1.3: ND(CD₃)₂ .. . DCI (1.5 equivalents) with DIPEA (4 equivalents); Stage 2.1: LiAlD₄(0.9 equivalents) in THF *and thus the synthesis of (undeuterated) DMT,described in the experimental section below

Analogously, the GMP-compatible chemistry of Scheme 2 was used to make asimilar series of 5-OMeDMT-based drug substances (see Scheme 4), eachselectively enriched with deuterium, some in accordance with formula (I)and others nevertheless of use in the present invention (for instance inits third aspect).

The compounds are described in the table below with the labelling againwith reference to formula (I) (in all compounds described below, n=1 andR¹=5-OMe):

R², R³ C(^(y)H)₂ Mwt Modification(s) to Scheme 4* (CH₃)₂ CH₂ 218.3 None(CH₃)₂ C(H)D 219.3 Stage 2.1:1:1 LiAlH₄:LiAlD₄ (0.9 equivalents of each)in THF (CH₃)₂ CD₂ 220.3 Stage 2.1: LiAlD₄ (0.9 equivalents) in THF(CD₃)₂ CH₂ 224.3 Stage 1.3: ND(CD₃)₂ . . . DCI (1.5 equivalents) withDIPEA (4 equivalents) (CD₃)₂ C(H)D 225.3 Stage 1.3: ND(CD₃)₂ . . . DCI(1.5 equivalents) with DIPEA (4 equivalents) Step 2.1:1:1 LiAlH₄:LiAlD₄(0.9 equivalents of each) in THF (CD₃)₂ CD₂ 226.3 Stage 1.3: ND(CD₃)₂ .. . DCI (1.5 equivalents) with DIPEA (4 equivalents) Stage 2.1: LiAlD₄(0.9 equivalents) in THF *and thus the synthesis of (undeuterated)5-OMeDMT, described in the experimental section below

In accordance with the third aspect of the invention is provided acomposition comprising a first compound, which is a compound orpharmaceutically acceptable salt thereof as defined in accordance withthe first aspect of the invention, and a second compound, which iseither (i) a compound or pharmaceutically acceptable salt thereof asdefined in accordance with the first aspect of the invention, but whichdiffers from the first compound through the identity of ^(y)H and/or theidentity of R³; or (ii) a compound or pharmaceutically acceptable saltthereof as defined in accordance with the first aspect of the invention,except that each ^(x)H and ^(y)H represent hydrogen.

Typically the second compound differs from the first compound onlythrough the identity of ^(y)H and/or the identity of R³; and/or ^(x)Hand ^(y)H representing hydrogen.

For example, the first and second compounds may differ through theidentity of ^(y)H, and in embodiments only through the identity of^(y)H. As is described in WO 2020/245133 A1 (Small Pharma Ltd), aquantifiable relationship exists between the extent of α-deuteration,and by proxy the H:D ratio of input reducing agent in the syntheticmethods disclosed therein, and the effect on potentiation of themetabolic half-life of DMT. Such technical information may be used toprepare compositions comprising pluralities of compounds of formula (I)described herein, in which the compounds or salts differ from each otheronly through the identity of ^(y)H.

It will be understood from the discussion above about syntheticmethodology that this may readily be achieved, in a controllable way, byusing mixtures of lithium aluminium hydride and lithium aluminiumdeuteride when reducing a precursor amide, the carbonyl group of whichis converted to the C(^(y)H)₂ portion of formulae (I) and (I′). Forexample, mixtures of compounds comprising controllable proportions ofcompounds of formula (I), in which n=0, which differ only by virtue ofα-mono- and/or α,α-di-deuteration (i.e. that differ only through theidentity of ^(y)H) may, if desired, be prepared by reducing2-(3-indolyl)-acetamide having the desired R² and R³ groups with adesired ratio of lithium aluminium hydride and lithium aluminiumdeuteride.

Alternatively or additionally, compounds (or pharmaceutically acceptablesalts thereof) in the composition of the third aspect of the inventionmay differ from each other through the identity of R³, for example onlythrough the identity of R³ and/or only through the identity of ^(y)H.Varying R³ may be achieved either where a compound is present in thecomposition in which R² is the same as R³, in which case this istypically but not necessarily CD₃; and another compound is present inwhich R³ is H.

The binding of dimethylamino-containing compounds of formula (I), thatis to say compounds of formula (I) in which R³ is not H, to serotoninreceptors within the body is expected to differ in selectivity andstrength to the binding of monomethylamino compounds of formula (I) i.e.in which R³ is H. Varying the relative amounts of dimethylamino- andmonomethylamino-containing compounds (in at least one of which theproportion of deuterium in a N-methyl group is greater than its naturalisotopic abundance and hydrogen) within compositions of the invention isexpected to allow modulation the pharmacodynamics and consequently thetherapeutic effect of the compositions. This offers a further element ofcontrol over the metabolism of compounds of formula (I).

Alternatively or additionally (to the composition comprising compoundsof formula (I) that differ through the identity of ^(y)H and/or R³ thatis), compositions of the third aspect of the invention may comprise acompound or pharmaceutically acceptable salt thereof as defined inaccordance with the first aspect of the invention, except for each ^(x)Hand ^(y)H representing hydrogen, in other words an analogue of acompound of formula (I) or pharmaceutically acceptable salt thereofwithout deuterium enrichment. As is set out in detail WO 2020/245133 A1(Small Pharma Ltd), supra), mixtures of DMT and alpha- and/orbeta-deuterated analogues thereof are described, together with theclinical usefulness. In the same way, mixtures of compounds of formula(I) and on deuterated analogues thereof may be used to modify,controllably, the pharmacokinetic profile of compounds of formula (Idescribed herein), thereby permitting more flexible therapeuticapplication.

Combining different compounds in these ways, whereby to providecompositions in accordance with the third aspect of the invention,provides additional variables, additional to increasing the proportionof deuterium atoms in the methyl groups of DMT or methyl group of NMTand their R¹-substituted derivatives that is, through which thepharmacodynamics of the parent undeuterated compounds corresponding tothose of formula (I) may be modified.

In particular, varying the relative amounts of the compounds within thecompositions of the invention may be expected to modulate thepharmacodynamics and consequently the therapeutic effect of thecompositions. Where these comprise compounds of formula (I) in which R³is H, for example, greater concentrations of these compounds may besusceptible to administration, since greater quantities ofmonomethyltryptamine compounds (to their dimethyltryptaminecounterparts) are generally tolerated in vivo. The relative amounts ofdifferent compounds within the compositions of the invention may bedetermined by a medical practitioner, based, in part on the metabolicprofile of the patient to whom the composition is intended to beadministered. For example, relatively greater amounts of compounds offormula (I) in which R³ is H may be more suitable for a patient with ahigher metabolism.

In some embodiments, the composition of the third aspect of theinvention comprises compounds of formula (I) in each of which one ^(y)His H and the other is D. In some embodiments, the composition comprisescompounds of formula (I) in each of which each ^(y)H is H. Sometimes,the composition comprises compounds of formula (I) in each of which each^(y)H is D.

For the avoidance of doubt, the above-mentioned embodiments do notexclude the presence of further compounds of formula (I) or undeuteratedanalogues thereof.

In particular embodiments, the composition of the third aspect of theinvention comprises two or three compounds of formula (I), which differfrom one another only by the definition of ^(y)H, i.e. providing apopulation of compounds of formula (I) in which the C(^(y)H)₂ moiety isCH₂, CD₂ or CH. In particular embodiments of these, NR²R³ is N(CD₃)₂ orN(CH₃)(CD₃), often N(CD₃)₂.

Compositions and of the invention may be quantified, at least partially,by their mean molecular weight. As used herein, mean molecular weightmeans the weighted average of molecular weights of a compound orcomposition (for example a composition comprising two or compounds offormula (I) differing only from one another by the extent ofdeuteration), as measured by an appropriate mass spectroscopictechnique, for example LC-MS SIM (selected-ion monitoring). In someembodiments, the mean molecular weight is the weighted average.

It will be understood that it will be possible to use mean molecularweights to characterise useful compounds and compositions of theinvention obtainable through the teachings herein, in particular byadjusting the relative proportions of lithium aluminium hydride andlithium aluminium deuteride in the reductions exemplified. It will befurther understood that the greater the extent of deuteration, thehigher the mean molecular weight of the composition.

In some embodiments, the composition consists essentially of compoundsof formula (I), optionally with undeuterated analogues thereof. Thismeans that the composition does not comprise material quantities ofother pharmaceutically active compounds, including otherdimethyltryptamine compounds. In other specific embodiments, thecomposition consists essentially of compounds of formula (I). In otherwords, and alternatively put, the compositions according to thesespecific embodiments constitute a drug substance comprising abiologically active ingredient consisting essentially of a mixture ofcompounds of formula (I).

According to particular embodiments, compositions of the invention, andused and for use in accordance with the relevant aspects of theinvention are absent material (e.g. detectable quantities ofdimethyltryptamine), in particular where one or both of R² and R³ areCD₃.

In some embodiments, the compositions of the invention have an oxygencontent of less than 2 ppm, such as between 0.1 ppm and 2 ppm. Theskilled person is able to determine the oxygen content of theformulation using any technique known in the art to be suitable, such asusing a dissolved oxygen meter (e.g. a Jenway 970 Enterprise DissolvedOxygen Meter, available from Keison Products:http://www.keison.co.uk/products/jenway/970.pdf. Compositions of theinvention having an oxygen content of less than 2 ppm are particularlyadvantageous for preparing dosage forms for administration via the oralor nasal cavities, as the reduced oxygen content ameliorates formationof malodourous impurities and/or degradation products from compounds offormula (I).

The composition may be stored in any suitable container. In someembodiments, to ameliorate degradation of the composition, compositionsof the invention are stored in a container adapted to preventpenetration of ultraviolet light, such as an amber glass vial. Inothers, the container within which the composition is stored is not soadapted (and may be, for example, made of clear glass) with protectionagainst ultraviolet light, if desired, provided by secondary packaging(for example packaging within which the receptacle containing theformulation may be placed).

To ameliorate degradation of the composition, it may be desirable tominimise the total oxygen content within the container in which thecomposition is stored, the oxygen within the container equilibratingbetween the composition and the headspace (if any) within the container.Accordingly, it may be desirable to store the composition under an inertatmosphere for example by purging the headspace to reduce its oxygencontent from about 20% typically found in air, to less than, forexample, 0.5%. Often, the container is airtight and the composition isstored under an inert atmosphere, such as under nitrogen or argon,typically nitrogen. The composition may be stored at room temperature,e.g. at about 20 to about 30° C. (typically about 20° C.) or at coolertemperatures, for example at about 2 to about 8° C. Alternatively, toameliorate degradation of the composition further, it may be stored attemperatures lower than room temperature, such as in a refrigerator orfreezer.

As described above, the invention provides in its fourth aspect apharmaceutical composition comprising a compound of formula (I), eitherdefined in accordance with the first aspect of the invention or inaccordance with the second aspect of the invention, or a composition inaccordance with the third aspect of the invention, in combination with apharmaceutically acceptable excipient.

Examples of pharmaceutically acceptable excipients that may be comprisedwithin the pharmaceutical composition of the invention include but arenot limited to those described in Gennaro et al., Remmington: TheScience and Practice of Pharmacy, 20^(th) Edition, Lippincott, Williamsand Wilkins, 2000 (specifically part 5: pharmaceutical manufacturing).Suitable pharmaceutically acceptable excipients are also described inthe Handbook of Pharmaceutical Excipients, 2^(nd) Edition; Editors A.Wade and P. J. Weller, American Pharmaceutical Association, Washington,The Pharmaceutical Press, London, 1994. M. F. Powell, T. Nguyen and L.Baloian provide a review of excipients suitable for parenteraladministration (administration other than by the mouth or alimentarycanal) in PDA J. Pharm. Sci. Technol., 52, 238-311 (1998). Compositionsinclude those suitable for oral, nasal, topical (including buccal,sublingual and transdermal), parenteral (including subcutaneous,intravenous and intramuscular) or rectal administration.

By means of pharmaceutically suitable liquids, the compositions of theinvention can be prepared in the form of a solution, suspension,emulsion, or as a spray. Aqueous suspensions, isotonic saline solutionsand sterile injectable solutions may be used, containingpharmaceutically acceptable dispersing agents and/or wetting agents,such as propylene glycol or butylene glycol.

The invention also provides a composition of the invention, incombination with packaging material suitable for the composition, thepackaging material including instructions for the use of thecomposition.

According to some embodiments, the pharmaceutical compositions of theinvention are suitable for parenteral administration, i.e. suitable foradministration other than by the mouth or alimentary canal, for exampleby inhalation or nasal, topical (including buccal, sublingual andtransdermal), subcutaneous, intravenous or intramuscular administration.By being suitable for (i.e. for) parenteral administration means thatsuch compositions are in accordance with Pharmacopeial requirements ofsterility, contaminants, and pyrogens (see for example The United StatesPharmacopeial Convention, General Requirements/

1

Injections, page 33). Sometimes, the pharmaceutical compositionscontains inhibitors of the growth of microorganisms (e.g. antimicrobialpreservatives) and/or anti-oxidants.

Pharmaceutical compositions suitable for injection typically have a pHof about 3 to 9 and an osmolality of about 250 to about 600 mOsm/Kg. pHvalues above 9 are reported by I. Usach et al. in Adv. Ther., 36,2986-2996 (2019) to relate to tissue necrosis (death of cells within thetissue), whereas values lower than 3 are reported to cause pain andphlebitis (inflammation of veins). Osmolality values greater than 600mOsm/Kg are also reported to cause pain.

As is described herein, the compounds and compositions of the inventionare anticipated to have greater oral bioavailability than a compoundcorresponding to one of formula (I) but without the deuterium enrichmentin a methyl group corresponding to R² or R³. According to particularembodiments, therefore, the pharmaceutical composition of the inventionis in the form of an oral dosage form.

By “oral dosage form” is meant a particular configuration (such as atablet or capsule, for example) comprising a particular dose of thecompound or composition, wherein the configuration is suitable for oraladministration. The oral dosage form may be a solid dosage form, such asa tablet, capsule, sachet, powder or granule, or a liquid or semi-solidoral dosage form such as a syrup, solution, ampoule, or dispersion.Typically, the oral dosage form is a solid dosage form, often a tabletor a capsule.

According to still further embodiments, the pharmaceutical compositionsof the invention are presented in a form suitable for inhalation.Inhalable formulations preferably comprise the compound of compounds offormula (I) in freebase form.

For the avoidance of doubt, an inhalable formulation is capable ofbecoming airborne and entering the lungs of a patient through the actionof the patient breathing in. In other words, inhalable formulations aresuitable for pulmonary administration. The inhalable formulation may beinhaled in the form of a vapour, aerosol or gas. Often, the inhalableformulation is inhaled in the form of a vapour or aerosol.

By “freebase” is meant that the amine within the compound of formula (I)or undeuterated analogues thereof (for example which may be present incompositions of the invention in addition to compounds of formula (I),as discussed above) are in their unprotonated form, as opposed to theconjugate acid (protonated) form of the amine. Accordingly, salts of thecompounds of formula (I) or undeuterated analogues thereof are excludedfrom the scope of the freebase. For the avoidance of doubt, zwitterionscomprising a protonated form of the amine and a negatively chargedsubstituent bound to the DMT (such as in the zwitterionic form ofpsilocybin) are excluded from the scope of the freebase.

Pharmaceutical compositions suitable for inhalation comprise a solventin which the freebase is at least partially soluble. The solvent istypically a liquid at ambient temperature and pressure (in particular atabout 20° C. and about 1 bar). In more particular embodiments, thesolvent is capable of forming a vapour or aerosol comprising thefreebase on the application of heat, for example the solvent may besuitable for use in an electronic vaping device (EVD). EVDs typicallyinclude a power supply section and a cartridge. The power supply sectionoften comprises a power source such as a battery, and the cartridgeoften comprises a heater and a reservoir capable of holding an inhalableformulation. The heater is typically contacted with the inhalableformulation (e.g. by a wick), and is typically configured to heat theinhalable formulation to generate a vapour or aerosol.

In some embodiments, the solvent is volatile (has a boiling point of≤100° C., such as 50 to 100° C.). Such solvents may be capable ofevaporation under the airflow of a vaporiser (such as a Volcano MedicVaporizer) at temperatures of 30 to 70° C., e.g. 55° C. Evaporation ofthe solvent leaves a residue of freebase, which may then be vapourisedinto a vapour or aerosol under the airflow of a vapouriser at highertemperatures (e.g. at temperatures of about 150 to 250° C., such as 210°C.), and inhaled.

In some embodiments, the solvent is any one or a combination of two ormore selected from the group consisting of propylene glycol(propane-1,2-diol), glycerine, polyethylene glycol, water, propanediol(propane-1,3-diol), butylene glycol (butane-1,3-diol), butane-2,3,-diol,butane-1,2-diol, ethanol and triacetin.

In some embodiments, the solvent is selected from propylene glycol,glycerine and polyethylene glycol, or a mixture thereof. Typically, thesolvent is a mixture of propylene glycol and glycerine in a ratio offrom about 50:50 (propylene glycol:glycerine) to about 10:90 by weight,such as about 50:50 to about 20:80 or about 50:50 to about 30:70 byweight. In some embodiments, the solvent is a mixture of propyleneglycol and glycerine in a ratio of from about 50:50 to about 30:70 byweight.

Often, the glycerine is vegetable glycerine, i.e. glycerine derived fromplant oils.

Pharmaceutical compositions suitable for inhalation or nasaladministration often comprise a taste-masking agent. The purpose of thetaste-masking agent is to make the taste or smell of the formulationmore appealing to the patient. In some embodiments, the pharmaceuticallyacceptable excipient comprises a taste-masking agent. When thepharmaceutically acceptable excipient comprises a solvent and ataste-masking agent, the taste-masking agent is typically at leastpartially soluble in the solvent and the solvent is often able to form avapour or aerosol comprising the freebase and the taste-masking agent onthe application of heat. Often, the taste-masking agent is suitable forvaporisation into a vapour or aerosol under the airflow of a vapouriser(e.g. at temperatures of about 150 to 250° C., such as 210° C.). Thetaste-masking agent is typically a liquid or a solid at ambienttemperature and pressure. It is advantageous that the taste-maskingagent has no adverse effect on the bioavailability of the freebase, e.g.it is advantageous that the freebase is stable when stored in thepresence of the taste-masking agent.

In some embodiments, the taste-masking agent is any one or a combinationof two or more selected from the group consisting of flavourings,glucose, fructose, sorbitol, mannitol, honey, saccharin, sucrose,xylitol, erythritol, maltitol, sucralose, neotame, trehalose andtagatose. In some embodiments, flavourings are menthol, vanilla,wintergreen, peppermint, maple, apricot, peach, raspberry, walnut,butterscotch, wild cherry, chocolate, anise, citrus such as orange orlemon, or liquorice flavourings.

Examples of further pharmaceutically acceptable excipients that may becomprised within the compositions suitable for inhalation or otherwiseinclude but are not limited to those described in Gennaro et. al.,Remmington: The Science and Practice of Pharmacy, 20^(th) Edition,Lippincott, Williams and Wilkins, 2000 (specifically part 5:pharmaceutical manufacturing). Suitable pharmaceutical excipients arealso described in the Handbook of Pharmaceutical Excipients, 2^(nd)Edition; Editors A. Wade and P. J. Weller, American PharmaceuticalAssociation, Washington, The Pharmaceutical Press, London, 1994. M. F.Powell, T. Nguyen and L. Baloian provide a review of excipients suitablefor parenteral administration in PDA J. Pharm. Sci. Technol., 52,238-311 (1998). All soluble excipients listed in this review article aresuitable excipients for use in inhalable formulations.

By means of pharmaceutically suitable liquids, the inhalableformulations can be prepared in the form of a solution, suspension,emulsion, or as a spray. Aqueous suspensions, isotonic saline solutionsand sterile injectable solutions may be used, containingpharmaceutically acceptable dispersing agents and/or wetting agents,such as propylene glycol or butylene glycol.

As described in detail herein, the invention is of therapeutic utility.In some embodiments, the therapy is psychedelic-assisted psychotherapy,i.e. the therapy associated with the first aspect of the invention istreatment of a mental disorder by psychological means, which areenhanced by one or more protocols in which a patient is subjected to apsychedelic experience induced by administration of the compound offormula (I).

In its fifth aspect, the invention provides a compound as defined in thefirst aspect, of the second aspect or composition of the third or fourthaspects for use in a method of treating a psychiatric or neurologicaldisorder in a patient.

In another aspect, the invention provides use of a compound as definedin the first aspect, of the second aspect or a composition of the thirdaspect for the manufacture of a medicament. In some embodiments of thisaspect, the medicament is for use in a method of treating a psychiatricor neurological disorder in a patient, including those disordersdescribed immediately hereinafter.

In some embodiments, the psychiatric or neurological disorder isselected from (i) an obsessive compulsive disorder, (ii) a depressivedisorder, (iii) a schizophrenia disorder, (iv) a schizotypal disorder,(v) an anxiety disorder, (vi) substance abuse, and (vii) an avolitiondisorder. Often, the psychiatric or neurological disorder is selectedfrom the group consisting of (i) an obsessive compulsive disorder, (ii)a depressive disorder, (iii) an anxiety disorder, (iv) substance abuse,and (v) an avolition disorder.

In some embodiments, the disorder is selected from the group consistingof major depressive disorder, treatment resistant major depressivedisorder, post-partum depression, an obsessive compulsive disorder andan eating disorder such as a compulsive eating disorder.

In some embodiments, the psychiatric or neurological disorder is majordepressive disorder. In some embodiments, the psychiatric orneurological disorder is treatment resistant depression.

In some embodiments, the therapy or method of treatment comprisesparenteral administration, such as inhalation or pulmonaryadministration of the formulation.

For the avoidance of doubt, embodiments related to fifth aspect of theinvention apply mutatis mutandis to the method of treatment of the sixthaspect of the invention. For example, the method may be to treat adisorder selected from the group consisting of (i) an obsessivecompulsive disorder, (ii) a depressive disorder, (iii) an anxietydisorder, (iv) substance abuse, and (v) an avolition disorder.

In order to treat the disorder, an effective amount of a compound offormula (I is administered, i.e. an amount that is sufficient to reduceor halt the rate of progression of the disorder, or to ameliorate orcure the disorder and thus produce the desired therapeutic or inhibitoryeffect.

Each and every reference referred to herein is hereby incorporated byreference in its entirety, as if the entire content of each referencewas set forth herein in its entirety.

The invention may be further understood with reference to the examplesthat follow.

EXAMPLES

Summary

A series of in vitro drug metabolism and pharmacokinetics (DMPK)experiments (Table 1) on N,N-dimethyltryptamine (DMT, SPL026), sixdifferent α,α,-bis-deuterium-N,N-dimethyltryptamine analogue blends(D₂DMT, SPL028i-SPL028vi), N,N-hexadeuterio-dimethyltryptamine (D₆DMT,SPL028vii) and α,α,bis-deuterio-N,N-hexadeuterio-dimethyltryptamine(D₈DMT, SPL028viii) were performed on human and animal tissue toinvestigate the metabolic profile and stability for each isotopicmixture (Table 2).

Comparisons of drug clearance in human liver hepatocyte andmitochondrial fractions indicate that deuterium enrichment of theα-carbon provides a rate limiting step in MAO-mediated oxidativedeamination of DMT analogues, which progressively increases with levelof α-deuteration.

CYP phenotyping indicated that SPL026 and two D₂-deuterated blends(SPL028i, SPL028ii) are substrates for the CYP2D6 and CYP2C19 enzymes.This result indicates an additional role of CYP-mediated metabolism ofDMT analogues, which could possibly contribute to the formation ofsecondary metabolites via the Noxidative pathway in vivo.

Deuterium substitution of DMT's methyl groups demonstrated an additionalDKIE which may be attributed to disruption of alternative metabolicpathways such as demethylation and N-oxidation, or via a secondary DKIEmechanism. Also notable is the absence of lower deuterated species D₀ toD₅ in SPL028vii and SPL028viii (see Table 2). This is advantageous foranalytical method development and validation and CMC aspects of drugproduct development of compounds and compositions of the presentinvention.

Experimental

A series of in vitro experiments (see Table 1 below) were conducted on arange of deuterium-enriched DMT compounds, SPL028i-SPL028viii, in orderto investigate the DKIE in human and animal tissue as a proxy of in vivoclearance.

TABLE 1 Summary of in vitro DMPK experiments with SPL026 and SPL028deuterated analogues Study Description Compounds tested Contribution ofMAO in vitro human hepatic intrinsic SPL026, clearance 6 × SPL028 (D₂)In vitro mouse hepatocytic intrinsic clearance SPL026, 6 × SPL028 (D₂)In vitro human hepatocytic intrinsic clearance SPL026, SPL028i (D₂),SPL028ii (D₂), SPL028vii (D6), SPL028viii (D₈) Contribution of MAO-A andMAO-B in vitro human SPL026 liver mitochondrial fraction intrinsicclearance In vitro human mitochondrial fraction intrinsic SPL026,SPL028i, SPL028iii, SPL028viii clearance In vitro human mitochondrialfraction intrinsic SPL026, SPL028i, SPL028ii, SPL028iii, SPL028vii,clearance SPL028viii CYP phenotyping against 8 human CYPs SPL026,SPL028i (D₂), SPL028ii (D₂)

TABLE 2 SPL026 and SPL028 deuterated analogues used in in vitro studies,detailing relative ratio of deuteration and calculated molecular weightfor each compound Cpd Weighted MW Name (g/mol) D₀ D₁ D₂ D₄ D₅ D₆ D₇ D₈SPL026 188.27 100 0 0 0 0 0 0 0 SPL028i 190.2398 0.70% 2.70% 96.60% 0 00 0 0 SPL028ii 189.1915 30.00% 48.30% 21.70% 0 0 0 0 0 SPL028iii189.6685 16.50% 46.80% 36.80% 0 0 0 0 0 SPL028iv 189.6764 9.30% 41.50%49.20% 0 0 0 0 0 SPL028v 188.9098 47.50% 41.30% 11.20% 0 0 0 0 0SPL028vi 188.9613 57.40% 35.30% 7.40% 0 0 0 0 0 SPL028vii 194.308 0.00%0 0 0.01% 1.20% 98.80% 0 0 SPL028viii 196.318 0.00% 0 0 0 0 0.10% 3.20%96.70%ChemistrySynthesis of DMT (SPL026)Stage 1: Coupling of indole-3-acetic acid and dimethylamine

To a 5 L vessel under N₂ was charged indole-3-acetic acid (257.0 g,1.467 mol), Hydroxybenzotriazole (HOBt) (˜20% wet) (297.3 g, 1.760 mol)and dichloromethane (DCM) (2313 mL) to give a milky white suspension.Ethylcarbodiimide hydrochloride (EDC·HCl) (337.5 g, 1.760 mol) was thencharged portion-wise over 5 minutes at 16-22° C. The reaction mixturewas stirred for 2 hours at ambient temperature before 2 M dimethylaminein tetrahydrofuran (THF) (1100 mL, 2.200 mol) was charged dropwise over20 minutes at 20-30° C. The resultant solution was stirred at ambienttemperature for 1 hour where HPLC indicated 1.1% indole-3-acetic acidand 98.1% stage 1. The reaction mixture was then charged with 10% K₂CO₃(1285 mL) and stirred for 5 minutes. The layers were separated, and theupper aqueous layer extracted with DCM (643 mL×2). The organic extractswere combined and washed with saturated brine (643 mL). The organicextracts were then dried over MgSO₄, filtered and concentrated in vacuoat 45° C. This provided 303.1 g of crude stage 1 as an off-white stickysolid. The crude material was then subjected to a slurry inmethyl-t-butyl ether (TBME) (2570 mL) at 50° C. for 2 hours before beingcooled to ambient temperature, filtered and washed with TBME (514 mL×2).The filter-cake was then dried in vacuo at 50° C. to afford stage 1266.2 g (yield=90%) as an off-white solid in a purity of 98.5% by HPLCand >95% by NMR.

Stage 2: Preparation of DMT

To a 5 L vessel under N₂ was charged stage 1 (272.5 g, 1.347 mol) andTHF (1363 mL) to give an off-white suspension. 2.4 M LiAlH₄ in THF(505.3 mL, 1.213 mol) was then charged dropwise over 35 minutes at20-56° C. to give an amber solution. The solution was heated to 60° C.for 2 hours where HPLC indicated stage 1 ND, stage 2 92.5%, Impurity 12.6%, Impurity 2 1.9%. The complete reaction mixture was cooled toambient temperature and then charged to a solution of 25% Rochelle'ssalts (aq.) (2725 mL) dropwise over 30 minutes at 20-30° C. Theresultant milky white suspension was allowed to stir at 20-25° C. for 1hour after which the layers were separated and the upper organic layerwashed with saturated brine (681 mL). The organic layer was then driedover MgSO₄, filtered and concentrated in vacuo at 45° C. The resultantcrude oil was subjected to an azeotrope from ethanol (545 mL×2). Thisprovided 234.6 g (yield=92%) of stage 2 in a purity of 95.0% by HPLCand >95% by NMR.

Stage 3a (i)-(iii): Preparation of Seed Crystals of DMT Fumarate

(i) Stage 2 (100 mg) was taken up in 8 volumes of isopropyl acetate andwarmed to 50° C. before charging fumaric acid (1 equivalent) as asolution in ethanol. The flask was then allowed to mature at 50° C. for1 hour before cooling to room temperature and stirring overnight,resulting in a white suspension. The solids were isolated by filtrationand dried for 4 hours at 50° C. to provide 161 mg of product (>99%yield). Purity by HPLC was determined to be 99.5% and by NMR to be >95%.

(ii) Substitution of isopropyl acetate for isopropyl alcohol in method(i) afforded a white suspension after stirring overnight. The solidswere isolated by filtration and dried for 4 hours at 50° C. to provide168 mg of product (>99% yield). Purity by HPLC was determined to be99.8% and by NMR to be >95%.

(iii) Substitution of isopropyl acetate for tetrahydrofuran in method(i) afforded a white suspension after stirring overnight. The solidswere isolated by filtration and dried for 4 hours at 50° C. to provide161 mg of product (>99% yield). Purity by HPLC was determined to be99.4% and by NMR to be >95%.

Analysis by x-ray powder diffraction, showed the products of each ofmethods 9i) to (iii) to be the same, which was labelled Pattern A.

Stage 3b: Preparation of DMT Fumarate

To a 5 L flange flask under N₂ was charged fumaric acid (152.7 g, 1.315mol) and Stage 2 (248.2 g, 1.315 mol) as a solution in ethanol (2928mL). The mixture was heated to 75° C. to give a dark brown solution. Thesolution was polish filtered into a preheated (80° C.) 5 L jacketedvessel. The solution was then cooled to 70° C. and seeded with Pattern A(0.1 wt %), the seed was allowed to mature for 30 minutes before coolingto 0° C. at a rate of 5° C./hour. After stirring for an additional 4hours at 0° C., the batch was filtered and washed with cold ethanol (496mL×2) and then dried at 50° C. overnight. This provided 312.4 g(yield=78%) of Stage 3 in a purity of 99.9% by HPLC and >95% by NMR.XRPD: Pattern A.

Synthesis of 5MeO-DMT

Stage 1: Coupling of 5-methoxyindole-3-acetic Acid and Dimethylamine

To a 100 mL 3-neck flask under N₂ was charged 5-methoxyindole-3-aceticacid (3.978 g, 19.385 mmol), HOBt (˜20% wet) (3.927 g, 23.261 mmol) andDCM (40 mL). EDC·HCl (4.459 g, 23.261 mmol) was then charged in portionsover 15 minutes at <30° C. The reaction mixture was stirred at ambienttemperature for 1 hour before being charged with 2 M dimethylamine(14.54 mL, 29.078 mmol) dropwise over 15 minutes at <25° C. Afterstirring for 1 hour HPLC indicated no starting material (SM, i.e.5-methoxyindole-3-acetic acid) remained. The reaction mixture was thencharged with 10% K₂CO₃ (20 mL), stirred for 5 minutes then allowed toseparate. The lower aqueous layer was removed and back extracted withDCM (10 mL×2). The organic extracts were combined, washed with saturatedbrine (10 mL) then dried over MgSO₄ and filtered. The filtrate wasconcentrated in vacuo at 45° C. to provide 3.898 g active (yield=87%) ofproduct in a purity of 95.7% by HPLC.

Stage 2: Preparation of 5MeO-DMT

To a 100 mL 3-neck flask under N₂ was charged stage 1 methoxy derivative(3.85 g, 16.586 mmol) and THF (19.25 mL). 2.4 M LiAlH₄ in THF (6.22 mL,14.927 mmol) was then charged dropwise over 30 minutes at <40° C. Thereaction mixture was heated to 60° C. for 1 hour where HPLC indicated0.1% SM (stage 1 methoxy derivative) remained. The reaction mixture wasthen cooled to ambient temperature and quenched into 25% Rochelle'ssalts (38.5 mL) dropwise over 30 minutes at <30° C. The resultantsuspension was stirred for 1 hour before being allowed to separate. Thelower aqueous layer was then removed, and the upper organic layer washedwith saturated brine (9.6 mL). The organics were then dried over MgSO₄,filtered and concentrated in vacuo before being subjected to anazeotrope from EtOH (10 mL×2). This provided 3.167 g active (yield=88%)of product in a purity of 91.5% by HPLC.

Stage 3: Preparation of 5MeO-DMT Fumarate

To a 50 mL 3-neck flask under N₂ was charged fumaric acid (1.675 g,14.430 mmol) and a solution of stage 2 methoxy derivative (3.15 g,14.430 mmol) in EtOH (37.8 mL). The mixture was then heated to 75° C.for 1 hour, this did not produce a solution as expected, the mixture wasfurther heated to reflux (78° C.) which still failed to provide asolution. The suspension was therefore cooled to 0-5° C., filtered andwashed with EtOH (8 mL×2) before being dried at 50° C. overnight. Thisprovided 3.165 g (yield=65%) of material in a purity of 99.9% by HPLC.

Synthesis of α,α-dideutero-5-Methoxydimethyltryptamine

For stage 1 (coupling of 5-methoxyindole-3-acetic acid anddimethylamine), see above.

Stage 2: Preparation of α,α-dideutero-5-Methoxydimethyltryptamine

To a 100 mL 3-neck flask under N₂ was charged stage 1 methoxy derivative(3.85 g, 16.586 mmol) and THF (19.25 mL). 2.4 M LiAlD₄ in THF (6.22 mL,14.927 mmol) was then charged dropwise over 30 minutes at <40° C. Thereaction mixture was heated to 60° C. for 1 hour where HPLC indicated0.1% SM (stage 1 methoxy derivative) remained. The reaction mixture wasthen cooled to ambient temperature and quenched into 25% Rochelle'ssalts (38.5 mL) dropwise over 30 minutes at <30° C. The resultantsuspension was stirred for 1 hour before being allowed to separate. Thelower aqueous layer was then removed, and the upper organic layer washedwith saturated brine (9.6 mL). The organics were then dried over MgSO₄,filtered and concentrated in vacuo before being subjected to anazeotrope from EtOH (10 mL×2). This provided 3.196 g active (yield=88%)of product in a purity of 91.5% by HPLC.

Stage 3: Preparation of α,α-dideutero-5-MethoxydimethyltryptamineFumarate

To a 50 mL 3-neck flask under N₂ was charged fumaric acid (1.675 g,14.430 mmol) and a solution of stage 2 methoxy derivative (3.15 g,14.430 mmol) in EtOH (37.8 mL). The mixture was then heated to 75° C.for 1 hour, this did not produce a solution as expected, the mixture wasfurther heated to reflux (78° C.) which still failed to provide asolution. The suspension was therefore cooled to 0-5° C., filtered andwashed with EtOH (8 mL×2) before being dried at 50° C. overnight. Thisprovided 3.165 g (yield=65%) of material in a purity of 99.9% by HPLC.

Synthesis of Deuterated Mixtures of DMT Compounds (SPL028i to SPL028vi)

A modified synthesis at stage 2 using solid LiAlH₄/LiAlD₄ mixtures wasadopted, using 1.8 equivalents of LiAlH₄/LiAlD₄ versus 0.9 equivalentsusing the process described above for undeuterated DMT.

Six deuteration reactions were performed.

Representative Synthesis of a Deuterated Mixture (Using 1:1LiAlH₄:LiAlD₄) of DMT Compounds

To a 250 mL 3-neck flask under N₂ was charged LiAlH₄ (1.013 g, 26.7mmol), LiAlD₄ (1.120 g, 26.7 mmol) and THF (100 mL). The resultantsuspension was stirred for 30 minutes before stage 1 (6 g, 29.666 mmol)was charged portion-wise over 15 minutes at 20-40° C. The reactionmixture was then heated to reflux (66° C.) for 2 hours where HPLCindicated no stage 1 remained. The mixture was cooled to 0° C. andquenched with 25% Rochelle's salts (aq) (120 mL) over 30 minutes at <30°C. The resultant milky suspension was stirred for 1 hour and thenallowed to separate. The lower aqueous layer was removed and the upperorganic layer washed with saturated brine (30 mL). The organics werethen dried over MgSO₄, filtered and concentrated in vacuo. This provided4.3 g of crude material. The crude was then taken up in ethanol (52 mL)and charged with fumaric acid (2.66 g, 22.917 mmol) before heating to75° C. The resultant solution was allowed to cool to ambient temperatureovernight before further cooling to 0-5° C. for 1 hour. The solids wereisolated by filtration and washed with cold ethanol (6.5 mL×2). Thefilter cake was dried at 50° C. overnight to provided 5.7 g (yield=63%)of product in a purity of 99.9% by HPLC and >95% by NMR.

Synthesis of d₆-DMT (SPL028vii)

Stage 1

EDC·HCl (15.7 g, 81.90 mmol) was added to 3-indoleacetic acid (12.0 g,68.50 mmol) and HOBt·H₂O (1.16 g, 75.75 mmol) in DCM (108 mL) at roomtemperature. The reaction was stirred for 1 hour after whichN,N-diisopropylethylamine (DIPEA) (35.6 mL, 205.75 mmol) andd₆-dimethylamine·HCl (9.0 g, 102.76 mmol) were added (temperaturemaintained below 30° C.). The reaction was stirred for 1 hour at roomtemperature after which analysis by HPLC indicated 65.6% product with28.9% 3-indoleacetic acid remaining. DIPEA (11.9 mL, 68.78 mmol) wasadded and the reaction was stirred for 1 hour at room temperature. HPLCindicated no change in conversion. Aqueous potassium carbonate (6.0 g in54 mL water) was added and the phases were separated. The aqueous phasewas extracted with DCM (2×30 mL). The combined organics were washed withbrine (2×30 mL) then aqueous citric acid (20 w/w %, 50 mL), dried overMgSO₄ and filtered. The filtrate was stripped and the resulting solidswere slurried in TBME (120 mL) and isolated by filtration. Purificationby flash column chromatography yielded 8.34 g of the desired product(58% yield). ¹H NMR confirmed the identity of the product.

Stage 2

LiAlH₄ (1 M in THF, 17.3 mL, 17.28 mmol) was added to a suspension ofstage 1 (4.0 g, 19.20 mmol) in THF (10 mL) at <30° C. The resultingreaction was heated to 60-65° C. and stirred for 2 hours. HPLC analysisindicated complete consumption of stage 1 with 97.3% product formed. Thereaction was cooled to room temperature and quenched into aqueousRochelle's salts (10 g in 30 mL water) at <30° C. After stirring for 1hour, the phases were separated. The aqueous phase was extracted withTHF (20 mL). The combined organics were washed with brine (20 mL), driedover MgSO₄, filtered and stripped (azeotroped with ethanol, 20 mL) togive the desired product as an amber oil (3.97 g). ¹H NMR confirmed theidentity of the product and indicated 8.5% ethanol was present (no THF)giving an active yield of 3.63 g, 97%.

Stage 3

d₆-DMT free base (3.6 g active, 18.53 mmol) was dissolved in ethanol (43mL) at room temperature. Fumaric acid (2.15 g, 18.53 mmol) was added andthe solution was heated to 75° C. (solids crystallised during heatingand did not re-dissolve). The resulting suspension was cooled to 0-5° C.and stirred for 1 hour. The solids were isolated by filtration, washedwith ethanol (2×7 mL) and pulled dry. Further drying in a vacuum oven at50° C. yielded the desired d₆-DMT fumaric acid salt (4.98 g, 87%).

Synthesis of d₈-DMT (SPL028viii)

For stage 1 (coupling of 3-indoleacetic acid and d₆-dimethylamine), seeabove

Stage 2

LiAlD₄ (1 M in THF, 17.3 mL, 17.28 mmol) was added to a suspension ofstage 1 (4.0 g, 19.20 mmol) in THF (10 mL) at <30° C. The resultingreaction was heated to 60-65° C. and stirred for 2 hours. HPLC analysisindicated complete consumption of the stage 1 with 97.3% product formed.The reaction was cooled to room temperature and quenched into aqueousRochelle's salts (10 g in 30 mL water) at <30° C. After stirring for 1hour, the phases were separated. The aqueous phase was extracted withTHF (20 mL). The combined organics were washed with brine (20 mL), driedover MgSO₄, filtered and stripped (azeotroped with ethanol, 20 mL) togive the desired product as an amber oil (4.01 g). ¹H NMR confirmed theidentity of the product and indicated 8.6% ethanol was present (no THF)giving an active yield of 3.66 g, 97%.

Stage 3

d₈-DMT free base (3.6 g active, 18.53 mmol) was dissolved in ethanol (43mL) at room temperature. Fumaric acid (2.15 g, 18.53 mmol) was added andthe solution was heated to 75° C. (solids crystallised during heatingand did not re-dissolve). The resulting suspension was cooled to 0-5° C.and stirred for 1 hour. The solids were isolated by filtration, washedwith ethanol (2×7 mL) and pulled dry. Further drying in a vacuum oven at50° C. yielded the desired d₈-DMT fumaric acid salt (4.62 g, 81%).

Assessment of Extents of Deuteration

This was achieved by LCMS-SIM (SIM=single ion monitoring), the analysisgiving a separate ion count for each mass for the deuteratedN,N-dimethyltryptamine compounds at the retention time forN,N-dimethyltryptamine. The percentage of each component was thencalculated from these ion counts.

For example, % D0=[D0/(D0+D1+D2)]×100.

HPLC Parameters

-   -   System: Agilent 1100/1200 series liquid chromatograph or        equivalent    -   Column: Triart Phenyl; 150×4.6 mm, 3.0 μm particle size (Ex:        YMC, Part number: TPH12S03-1546PTH)    -   Mobile phase A: Water:Trifluoroacetic acid (100:0.05%)    -   Mobile phase B: Acetonitrile:Trifluoroacetic acid (100:0.05%)

Gradient: Time % A % B 0 95 5 13 62 38 26 5 95 30.5 5 95 31 95 5 Flowrate: 1.0 mL/min Stop time: 31 minutes Post runtime: 4 minutes Injectionvolume: 5 μL Wash vial: N/A Column: 30° C. combined temperatureWavelength: 200 nm, (4 nm) Reference: N/A

Mass Spectrometry Parameters

System: Agilent 6100 series Quadrupole LC-MS or equivalent Drying gasflow: 12.0 L/min Drying gas temp.: 350° C. Nebuliser pressure: 35 psigFragmentor: 110 Gain: 1.00

Cpd RT RRT Conc Diluent Detection Mass D0 10.64 1.00 0.30 mg/mlCH₃CN:H₂O (+) SIM 189.10 m/z (50:50) D1 10.64 1.00 0.30 mg/ml CH₃CN:H₂O(+) SIM 190.10 m/z (50:50) D2 10.64 1.00 0.30 mg/ml CH₃CN:H₂O (+) SIM191.10 m/z (50:50) MS-SIM range is the target mass ±0.1 m/zHuman Hepatocyte Intrinsic Clearance

In vitro determination of intrinsic clearance (Clint) is a valuablemodel for predicting in vivo clearance. The liver contains both phase Iand phase II drug metabolising enzymes, which are present in the intactcell and thereby provides a valuable model for the study of drugmetabolism. In particular CLint in hepatocytes is a measure of thepotential of a compound to undergo metabolism and can be related tohepatic clearance in vivo by also taking into consideration plasmaprotein binding and liver blood flow. Therefore, CLint may be used as anindex of the relative metabolic stability of compounds and compared withother external probe substrates. Furthermore, the measurement of CLintin vitro, where hepatic metabolic clearance is known to be an issue, maybe a useful means of understanding the different pharmacokineticbehaviour of compounds in vivo.

Assay Method

Human (mixed gender) hepatocytes pooled from 10 donors were used toinvestigate the in vitro intrinsic clearance of SPL026 and SL028analogues in three separate experiments:

-   -   First experiment—Human (Mixed Gender) Hepatocytes; 0.545 million        cells/mL. Final organic concentration 1.05% consisting of 80.74%        of MeCN and 19.26% DMSO    -   Second experiment—Human (Mixed Gender) Hepatocytes; 0.427        million cells/mL. Final organic concentration 1% consisting of        84.7% of MeCN and 15.3% DMSO.    -   Third experiment—Human (Mixed Gender) Hepatocytes; 0.362 million        cells/mL

Mouse CD-1 (Male) Hepatocytes

-   -   Final organic concentration 1% consisting of 84.7% of MeCN and        15.3% DMSO        Assay Preparation    -   Hepatocyte buffer is prepared as 26.2 mM NaHCO₃, 9 mM Na HEPES,        2.2 mM D-Fructose and DMEM in MilliQ water.    -   Compound and marker stocks are prepared at 10 mM in DMSO and        further diluted to 100× the assay concentration in 91:9        acetonitrile:DMSO.    -   Hepatocytes are thawed rapidly in a water bath at 37° C. and,        once just thawed, decanted into hepatocyte buffer. Cells are        centrifuged and the supernatant removed before counting and        resuspension at the final assay concentration.        Assay Procedure

A concentration of 5 μM was used for all test compounds, as well assumatriptan, serotonin, benzylamine controls with 2 replicateincubations per compound in each experiment. This concentration waschosen in order to maximise the signal-to-noise ratio, while remainingunder the Michaelis constant (K_(m)) for the monoamine oxidase enzyme(MAO). Diltiazem and diclofenac controls were used at alaboratory-validated concentration of 1 μM.

Hepatocytes are added to pre-warmed incubation tubes (37° C.).Pre-prepared 100× assay compound stocks are then added to the incubationtubes and mixed carefully. Samples are taken at 7 time points (2, 4, 8,15, 30, 45 and 60 minutes). At each timepoint, small aliquots werewithdrawn from the incubation and quenched 1:4 with ice-cold acidifiedmethanol or acetonitrile containing internal standard.

Incubation tubes are orbitally shaken at 37° C. throughout theexperiment.

Standard final incubation conditions are 1 μM compound in buffercontaining nominally ˜0.5 million viable cells/mL, ˜0.9% (v/v)acetonitrile (MeCN) and ˜0.1% (v/v) DMSO (specific assay concentrationsoutlined above, section 2).

Quenched samples are mixed thoroughly, and protein precipitated at −20°C. for a minimum of 12 hours. Samples are then centrifuged at 4° C.Supernatants are transferred to a fresh 96-well plate for analysis.

Liquid Chromatography-Mass Spectrometry (LC-MS/MS)

The following LC-MS/MS conditions were used for the analysis:

-   -   Instrument: Thermo TSQ Quantiva with Thermo Vanquish UPLC system    -   Column: Luna Omega 2.1×50 mm 2.6 μm    -   Solvent A: H₂O+0.1% formic acid    -   Solvent B: Acetonitrile+0.1% formic acid    -   Flow rate: 0.8 ml/min    -   Injection vol: 1 μl    -   Column temp: 65° C.    -   Gradient:

Time % (mins) Solvent B 0.00 5.0 0.90 75.0 1.36 99.0 1.36 5.0 1.80 5.0

-   -   MS parameters:    -   Positive ion spray voltage: 4000 V    -   Vaporiser temperature: 450° C.    -   Ion transfer tube temp: 365° C.    -   Sheath gas: 54    -   Aux gas: 17    -   Sweep gas: 1    -   Dwell time 8 ms    -   MRM transitions:    -   D0=mass to charge ratio 189.136>144.179 (method determined from        SPL026 analysis)    -   D1=mass to charge ratio 190.136>59.17 (method determined from        SPL028ii analysis)    -   D2=mass to charge ratio 191.137>60.169 (method determined from        SPL028i analysis)    -   D6=mass to charge ratio 195.17>64.127    -   D8=mass to charge ratio 197.2>146.17

The MRM transitions were determined from a preliminary analysis of DMTsamples containing either no deuterium (for D0 transition), or highlevels of either D1, D2, D6 or D8 deuteration (for the D1, D2, D6 and D8transitions respectively).

The resulting concentration-time profile was then used to calculateintrinsic clearance (CLint) and half-life (t½). To do this, the MS peakarea or MS peak area/IS response of each analyte is plotted on a naturallog scale on the y axis versus time (min) of sampling on the X axis. Theslope of this line is the elimination rate constant. This is convertedto a half-life by −ln(2)/slope. Intrinsic clearance is calculated fromthe slope/elimination rate constant and the formula isCLint=(−1000*slope)/cell density in 1E6 cells/ml, to give units ofmicrolitre/min/million cells.

Clearance of Six Different D₂DMT Analogue Blends (SPL028i-SPL028vi) Withand Without MAO Inhibitors

The contribution of MAO of six differentα,α,-bis-deuterium-N,N-dimethyltryptamine (D₂DMT) compounds was examinedusing an irreversible, combined MAO-A/B inhibitor (100 nM clorgyline and100 nM Deprenyl/Selegiline added as a cassette) via the measurement ofin vitro intrinsic clearance using human (mixed gender) hepatocytes from10 donors (0.545 million cell s/mL; final organic concentration 1.05%consisting of 80.74% of MeCN and 19.26% DMSO).

Effect of Deuteration

Data were fitted with two separate linear models using linear regressionanalyses (one-way ANOVA), which revealed that deuterium enrichment atthe α-carbon of DMT decreases intrinsic clearance linearly withincreasing percentage of D₂-deuteration using the formula:y=D₂*−6.04+12.9, r²=0.748 and molecular weight (MW) using the formula:y=MW*79.5+98.8, r²=0.811.

96.6% D₂-DMT (SPL028i) saw the biggest change in metabolic stability,˜2-fold change in intrinsic clearance and half-life compared to SPL026in initial hepatocyte studies (Table 3 and Table 4). The metabolicstability of intermediate blends of deuteration (SPL028ii-SPL028vi)increased in a manner which correlated with increasing level ofdeuteration and molecular weight (Table 3 and Table 4).

TABLE 3 In vitro Intrinsic clearance of SPL026 and 6 differentD₂-deuterated SPL028 analogue blends in in human hepatocytes,highlighting the fold change in intrinsic clearance from SPL026 for eachdeuterated compound, with and without inhibitors. Compounds ordered viamolecular weight. Intrinsic clearance (μL/min/million cells) Ratio ofFold Fold Cpd Molecular deuteration Without change from With change fromname weight (D₀:D₁:D₂) inhibitors SPL026 inhibitors SPL026 SPL026 188.27100:0:0 13.77 1.00 13.24 1.00 SPL028v 188.9098 48:41:11 10.99 1.25 9.511.39 SPL028vi 188.9613 57:35:7 13.64 1.01 10.79 1.23 SPL028ii 189.191530:48:22 10.46 1.32 8.78 1.51 SPL028iii 189.6685 17:47:37 9.36 1.47 6.901.92 SPL028iv 189.6764 9:42:49 11.14 1.24 7.46 1.77 SPL028i 190.23981:3:97 7.15 1.93 7.50 1.77 Benzylamine 16.70 <3.0 Serotonin 38.60 10.10

TABLE 4 In vitro half-life of SPL026 and 6 different D₂-deuteratedSPL028 analogue blends in in human hepatocytes, highlighting the foldchange in intrinsic clearance from SPL026 for each deuterated compound,with and without inhibitors. Compounds ordered via molecular weight.Ratio of Fold Fold Molecular deuteration Without change from With changefrom Cpd name weight (D₀:D₁:D₂) inhibitors SPL026 inhibitors SPL026SPL026 188.27 100:0:0 92.39 1.00 96.06 1.00 SPL028v 188.9098 48:41:11119.61 1.29 135.10 1.41 SPL028vi 188.9613 57:35:7 95.04 1.03 119.62 1.25SPL028ii 189.1915 30:48:22 125.80 1.36 147.47 1.54 SPL028iii 189.668517:47:37 140.43 1.52 189.60 1.97 SPL028iv 189.6764 9:42:49 116.84 1.26171.17 1.78 SPL028i 190.2398 1:3:97 178.79 1.94 169.75 1.77 Benzylamine76.30 460.00 Serotonin 33.00 125.70Contribution of MAO (See Also FIG. 2 )

Two-way ANOVA was carried out to determine the influence of MAOinhibitors and compound deuteration on intrinsic clearance. There was asignificant effect of MAO inhibitors on intrinsic clearance F(1,6)=11.42, p=0.0149, and deuteration on intrinsic clearance F(1,6)=9.996,p=0.006.

The inclusion of MAO inhibitors was shown to have minimal effect on themetabolism of SPL026 (DMT) resulting in ˜4% slower intrinsic clearance(Table 5). MAO inhibitors were also shown to have a small effect on the96.6% D₂-deuterated analogue (SPL028i) which saw a ˜5% quicker intrinsicclearance in the presence of MAO inhibitors (Table 5). These resultsindicate that MAO enzymes do not significantly contribute to themetabolism of SPL026 and SPL028i in human liver hepatocytes.

MAO inhibitors were shown to have a greater inhibitory effect onintrinsic clearance for the remaining five D₂-deuterated analogue blends(SPL028ii-SPL028vi). For these five compounds, the inhibitory action ofMAO inhibitors was shown to increase linearly with increasing level ofdeuteration and molecular weight, with the exception of SPL028vi (Table3). 49% D₂-deuterated SPL028iv saw the largest change in intrinsicclearance (49%) with the inclusion of MAO inhibitors (Table 5), whereas36.8% D₂-deuterated SPL028iii saw the largest change (˜2 fold) inmetabolic stability relative to SPL026 in cellular fractions withinhibitors (Table 3 and 4).

TABLE 5 In vitro Intrinsic clearance and half-life of SPL026 and 6different D₂-deuterated SPL028 analogue blends in in human hepatocyteswith and without MAO-A/B inhibitor combination. Percentage change (%)values represent the % change in metabolic stability with the inclusionof MAO inhibitors vs no inhibitors, measured by intrinsic clearance andhalf- life separately. Compounds are ordered by increasing molecularweight. Intrinsic clearance Ratio of (μL/min/million cells) Half-life(min) Cpd Mol. deuteration Without With % Without With % Name weight(D₀:D₁:D₂) inhibitors inhibitors change inhibitors inhibitors changeSPL026 188.27 100:0:0 13.77 13.24 −4.00 92.39 96.06 3.82 SPL028v188.9098 48:41:11 10.99 9.51 −15.56 119.61 135.1 11.47 SPL028vi 188.961357:35:7 13.64 10.79 −26.41 95.04 119.62 20.55 SPL028ii 189.1915 30:48:2210.46 8.78 −19.13 125.8 147.47 14.69 SPL028iii 189.6685 17:47:37 9.366.9 −35.65 140.43 189.6 25.93 SPL028iv 189.6764 9:42:49 11.14 7.46−49.33 116.84 171.17 31.74 SPL028i 190.2398 1:3:97 7.15 7.5 4.67 178.79169.75 −5.33 Benzylamine 16.7 <3.0 <−450 76.3 460 >83.41 Serotonin 38.610.1 −282.18 33 125.7 73.75

These results indicate that increasing the level of deuteration at theα-carbon of DMT decreases the MAO enzyme metabolism of the compound.

Clearance of Six D₂DMT Analogue Blends (SPL028i-SPL028vi) and One D₆-DMT(SPL028vii) Analogue Blends

In vitro human hepatic intrinsic clearance of the six differentα,α,-bis-deuterium-N,N-dimethyltryptamine (D₂DMT) compounds and oneN,N-hexadeuterio-dimethyltryptamine (D₆DMT, SPL028vii) were measured toinvestigate the effects of methyl group deuteration vs α-carbondeuteration on metabolic stability in using human (mixed gender)hepatocytes from 10 donors (0.427 million cells/mL; final organicconcentration 1% consisting of 84.7% of MeCN and 15.3% DMSO).

TABLE 6 In vitro intrinsic clearance and half-life of 6 differentD₂-deuterated DMT and D₈-deuterated DMT analogue blends in humanhepatocytes, ordered by increasing level of molecular weight Intrinsicclearance Compound Name (μL/min/million cells) Half-life (min) SPL028v14.1 119 SPL028vi 13.4 126.8 SPL028ii 9.1 191.1 SPL028iii 8.2 213.9SPL028iv 7.7 223.9 SPL028i 6.3 258.3 SPL028vii (D₆) 13.3 122.2 Diltiazem(A) 15.3 15.0 Diltiazem (B) 17.2 18.2 Diclofenac (A) 155.0 154.0Diclofenac (B) 150.1 154.3

Data fitted with a linear regression model on the six differentD₂-deuterated confirmed previous findings that deuterium enrichment atthe α-carbon of DMT decreases intrinsic clearance linearly withincreasing level of D₂-deuteration, y=D₂*−8.07+12.9, r²=0.690 andmolecular weight. A linear regression model was also fitted by molecularweight using formula: y=MW*13.9+6.06, r²=0.923 revealing molecularweight is a strong predictor of intrinsic clearance for the 6 differentD₂-deuterated SPL028 blends.

Initial hepatocyte data did not suggest a relationship between molecularweight and intrinsic clearance of D₂-deuterated and D₆-deuterated SPL028blends, r²=0.0395.

Clearance of Two D₂DMT (SPL028i and SPL028ii), One D₆DMT (SPL028vii) andOne D₈-DMT (SPL028viii) Analogue Blends

Further human hepatocyte assays were conducted with two D₂-deuteratedSLP028 analogue blends and two additional deuterated analogues: D₆DMTand D₈DMT to measure in vitro intrinsic clearance using human (mixedgender) hepatocytes from 10 donors (0.362 million cells/mL).

TABLE 7 In vitro intrinsic clearance and half-life of two differentD₂-deuterated DMT, D₆-deuterated DMT and D₈-deuterated DMT analogueblends in human hepatocytes, ordered by increasing level of molecularweight Intrinsic Clearance Compound (μL/min/ Fold change Half- Foldchange Name million cells) from SPL026 life (min) from SPL026 SPL02619.4 1.0 98.9 1.0 SPL028ii 11.7 1.7 170.9 1.7 SPL028i 8.3 2.3 233.1 2.4SPL028vii 17.1 1.1 112.1 1.1 SPL028viii 9.3 2.1 206.9 2.1 Diltiazem 22.087.3 Diclofenac 92.5 20.7

A linear regression model did not support a predictive relationshipbetween molecular weight and intrinsic clearance for SPL026, SPL028i,SPL028ii, SPL029vii and SPL028viii, r²=0.0445.

In agreement with hepatocyte results presented above, deuteration of themethyl group in D₆-deuterated SPL028vii appeared not to effect intrinsicclearance in human hepatocytes relative to SPL026. Intrinsic clearanceof SPL026 (19.4 μL/min/million cells)−Intrinsic clearance of SPL028vii(17.1 μL/min/million cells)=2.3 μL/min/million cells.

Complete deuterium enrichment at both the α-carbon and methyl group ofDMT in the D₈-deuterated SPL028viii compound also appeared not tosignificantly change metabolic stability relative to 96.6% α-carbonD₂-deuterated SPL028i analogue. Intrinsic clearance of SPL028i (8.3μL/min/million cells)−Intrinsic clearance of SPL028viii (9.3μL/min/million cells)=1.0 μL/min/million cells.

In Vitro Mouse Hepatocytic Intrinsic Clearance

The in vitro intrinsic clearance of six different D₂-deuterated SPL028analogues blends relative to SPL026 was performed using mouse (maleCD-1) hepatocytes (0.367 million cells/mL; final organic concentration1% consisting of 84.7% of MeCN and 15.3% DMSO).

Data was compared to in vitro human hepatocyte intrinsic clearanceresults to assess the suitability of an in vivo mouse model to predicthuman metabolism of SPL026 and SPL028 compounds. A concentration of 5 μMwas used for all test compounds, as well as serotonin, benzylamine,diltiazem and diclofenac internal controls with 2 replicate incubationsper compound.

TABLE 8 In vitro half-life and intrinsic clearance of SPL026 and 6 ×D₂-deuterated SPL028 deuterated compounds in mouse hepatocytes.Compounds ordered by increasing molecular weight. w Intrinsic clearanceCompound (μL/min/ Fold change w Half- Fold change Name million cells)from SPL026 life (min) from SPL026 SPL026 123.5 1.00 15.3 1.00 SPL028v117.7 1.05 16.1 1.05 SPL028vi 114.0 1.08 16.6 1.08 SPL028ii 102.7 1.2018.4 1.20 SPL028iii 106.2 1.16 17.9 1.17 SPL028iv 106.9 1.16 17.7 1.16SPL028i 97.4 1.27 19.4 1.27 Serotonin 83.0 22.8 Benzylamine 134.1 14.3Diltiazem >460.0 <3.0 Diclofenac 57.7 34.1Use of Liver Mitochondrial Fraction to Model Human Metabolism ofDeuterated DMT

Given the predicted 5 minute half-life of DMT in humans, the inventorsexpect that DMT is largely broken down before reaching the human liver.Therefore, an alternative in vitro assay was selected as a moreappropriate system to model human metabolism of DMT. The followingassays conducted on Human Liver Mitochondrial (HLMt) fractions predictenhanced fold-change between SPL026 and D₂-deuterated SPL028i comparedwith the fold-change predicted in hepatocyte studies. Moreover, anadditional protective effect is observed between D₂-deuterated SPL028iand D₈-deuterated SPL028viii, supportive of a synergistic effect onmitochondrial metabolism when both the α-carbon and methyl group(s) ofDMT and DMT analogues of formula (I) are deuterated.

Contribution of MAO-A and MAO-B In Vitro Human Liver MitochondrialFraction Intrinsic Clearance

Human Liver Mitochondrial (HLMt) fractions contain high quantities ofMAO enzymes and therefore, provide a useful tool to measure theclearance of MAO substrates.

A series of investigations using HLMts were conducted to assess theeffect of MAO on the metabolism of DMT and deuterated DMT analogues invitro.

In Vitro Human Mitochondrial Fraction Intrinsic Clearance of SPL026(DMT) With/Without MAO-A and MAO-B Inhibitors

In vitro determination of the intrinsic clearance of SPL026 withselective and irreversible MAO-A inhibitor (100 nM clorgyline) and MAO-Binhibitor (100 nM Deprenyl/Selegiline) were added separately to 0.5mg/mL of human liver mitochondrial fraction. The MAO-A substrate,Serotonin and MAO-B substrate, Benzylamine were added as positivecontrols which confirmed the presence of MAO-A and MAO-B and the actionof Clorgyline and Deprenyl inhibitors.

TABLE 9 Intrinsic clearance and half-life of SPL026 in human livermitochondrial fraction Compound Intrinsic Clearance Name Inhibitor(μL/min/mg protein) Half-life (min) SPL026 DMSO Vehicle 42.9 33.7 SPL026Clorgyline <3.9 >373.7 (MAO-A inhibitor) SPL026 Deprenyl 42.7 32.5(MAO-B inhibitor) Serotonin DMSO Vehicle 124.6 11.1 Serotonin Clorgyline<3.3 >420.2 Benzylamine DMSO Vehicle 45.7 30.4 Benzylamine Deprenyl <3.3>420.2

SPL026 half-life and intrinsic clearance significantly increased withMAO-A inhibitor (Clorgyline), resulting in a 11-fold increase inintrinsic clearance compared data from SPL026 without MAO inhibitors.Deprenyl (MAO-B inhibitor) showed no difference in human mitochondrialintrinsic clearance relative to fraction without inhibitors. Theseresults suggest that a role of MAO-A but not MAO-B, in the metabolism ofSPL026.

In Vitro Human Mitochondrial Fraction Intrinsic Clearance of SPL026(DMT), SPL028i (96.6% D₂-DMT), SPL028iii (36.8% D₂-DMT) and SPL028viii(D₈-DMT)

In vitro determination of the intrinsic clearance of SPL026, SPL028i,SPL028iii and SPL028viii were added separately to 0.5 mg/mL of humanliver mitochondrial fraction. The MAO-A substrate ‘Serotonin’ and MAO-Bsubstrate ‘Benzylamine’ were added as positive controls and confirmedthe presence of MAO-A and MAO-B.

TABLE 10 Intrinsic clearance and half-life of SPL026, SPL028i,SPL028iii, SPL028viii in human liver mitochondrial fraction IntrinsicClearance Compound (μL/min/ Fold change Half- Fold change Name mgprotein) from SPL026 life (min) from SPL026 SPL026 161.0 1.0 8.6 1.0SPL028iii 15.0 3.6 31.1 3.6 SPL028i 44.6 10.7 92.8 10.8 SPL028viii 10.914.8 127.7 14.8 Serotonin 151.0 — 9.2 — Benzylamine 60.0 — 23.2 —

Half-life and intrinsic clearance increased with increasing level ofdeuteration for the SPL028 compounds, when compared to SPL026.D₈-deuterated SPL028viii saw the greatest change in clearance (14.8 foldincrease) relative to SPL026. 96.6% D₂-deuterated SPL028i also showed alarge change (10.7 fold increase) in clearance compared to SPL026.36.80% D₂-deuterated SPL028iii demonstrated a smaller change (3.6 foldincrease) in clearance compared to SPL026.

Cytochrome P450 (CYP) Phenotyping Against 8 Human CYPs

The members of the Cytochrome P450 (CYP) superfamily are considered themost important drug metabolising enzymes. A detailed understanding ofthe contribution of individual CYPs towards the clearance of a drugcandidate is important to 8 in the production and understanding ofpotential drug-drug interactions.

Some CYP isoforms, e.g. CYP2D6, CYP2C9, CYP2C19, known to be polymorphicleading to significant intra-individual variability in the ratemetabolism, which can alter drug exposure significantly and, as aconsequence, affect drug efficacy and safety.

The CYPs used in this study are heterologously expressed in E. coli andpurchased as individualised forms (CYP bactosomes) from CYPEX.Bactosomes contain recombinant CYP isoenzymes combined with CYPreductase leading to a higher specific activity than liver microsomes.As many as 18 human CYPs plus a variety of CYPs from preclinical speciesalong with other drug-metabolising enzymes are currently commerciallyavailable.

Assay Method

Preparation

Phosphate buffer is prepared at 0.1 M, pH 7.4 by combining 0.1 M Na₂HPO₄and 0.1 M KH₂PO₄ solutions.

Compound and marker stocks are prepared at 10 mM and DMSO and furtherdiluted to 100× the assay concentration in DMSO.

Nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salthydrate (NADPH) is prepared at 10 m<in 0.1 M phosphate buffer (pH 7.4).

The individual CYP bactosomes are thawed at room temperature undilutedto 200 pmol/mL and 0.1 M phosphate buffer.

Procedure

Pre-prepared 100× assay compound stocks/markers, and 2× assay CYPbactosomes are added to incubation tubes, mixed and pre-warmed at 37° C.for 5 minutes. Pre-warmed NADPH is then added to the incubation tubesand mixed well. Samples were taken at predetermined time points. At eachtime point, a sample is removed from incubation and quenched 1:4 withice-cold methanol or acetonitrile containing internal standard.Incubation tubes are orbitally shaken at 37° C. throughout theexperiment.

Standard final incubation conditions are 1-3 μM compound in a buffercontaining 100 pmol/mL CYP bactosome, 1% (v/v) DMSO.

Quenched samples are mixed thoroughly and protein precipitated at −20°C. for a minimum of 12 hours. Samples were then centrifuged at −4° C.Supernatants are transferred to a fresh 96-well plate for analysis.

Positive control markers are as specified in Table 11.

TABLE 11 Positive control markers used for the determination ofmetabolic intrinsic clearance by 8 human CYP isoforms CYP450 Positivecontrols 1A2 Carvedilol Tacrine 2B6 Bupropion Ticlopidine 2C8Montelukast Verapamil 2C9 Carvedilol Diclofenac 2C19 CarvedilolPropranolol 2D6 Carvedilol Dextromethorphan 3A4 Carvedilol Midazolam 3A5Midazolam VerapamilData Processing

The elimination rate constant (k) is calculated using the slope of a ln(MS peak area or response—if internal standard is used) vs. time plot ofthe test compounds and markers.

Intrinsic clearance in μL/min/nmol CYP is calculated using the followingequation:Clint=−1000 k/CYP concentration

Projected CYP isoform intrinsic clearance accounting for estimated CYPabundance in human liver microsomes (μL/min/mg microsomal protein)* iscalculated using the following equation:Projected set isoform intrinsic clearance=Estimated CYP abundance*Clint* Estimated CYP abundance is taken as an average from three literaturereferences 1, 2 3 and the abundances used are as follows (nmol CYP/mgHuman Liver Microsomal Protein):

CYP450 1A2 2B6 2C8 2C9 2C19 2D6 3A4 3A5 Abundance 0.032 0.023 0.0240.060 0.009 0.012 0.075 0.009 (nmol CYP/mg H mic proteinReference 1: McGinnty et al. (2000) Automated definition of theenzymology of drug oxidation by the major human drug metabolizingcytochrome P450s, Drug Metabolism and Disposition, 28, 1327-1334Reference 2: Ohtsuki et al. (2012), Simultaneous Absolute ProteinQuantification of Transporters, Cytochromes P450 andUDP-Glucuronosyltransferases as a Novel Approach for theCharacterization of Individual Human Liver: Comparison with mRNA Levelsand Activities, Drug Metabolism and Disposition, 40, 83-92Reference 3: Achour et al. (2014) Simultaneous Quantification of theAbundance of Several Cytochrome P450 and Uridine59-Diphospho-Glucuronosyltransferase Enzymes in Human Liver MicrosomesUsing Multiplexed Targeted Proteomics, Drug Metabolism and Disposition,42, 500-510 (guidelines and example)

CYP phenotyping was conducted to investigate the contribution of CYPisoforms in the metabolism of SPL026 and 2 different D2-deuteratedSPL028 analogues (SPL028i, SPL028ii) and the positive controls mentionedin Table 11 above.

Intrinsic clearance, half-life and projected intrinsic clearance of 8human CYPs (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A5) inE. coli CYPEX membranes with SPL026 and 2× SPL028 D₂-deuterated analogueblends are presented in Tables 12-14.

CYP2D6 had the largest effect on intrinsic clearance of SPL026 and2-D₂-deuterated DMT analogues (SPL028i and SPL028ii). CYP2C19 had asmall effect on the intrinsic clearance of all three tested compounds.No significant difference in CYP2C₁₉ intrinsic clearance or half-lifebetween SPL026, SPL028i and SPL018ii was found as determined by one-wayANOVA (F(2,3)=0.769, p=0.538) and (F(2,3)=0.789, p=0.530), respectively.There was also no significant difference in CYP2D6 intrinsic clearanceor half-life between SPL026, SPL028i and SPL028ii as determined byone-way ANOVA (F(2,3)=0.510, p=0.644) and (F(2,3)=0.512, p=0.644)respectively.

No turnover of any other CYP isoform (1A2, 2B6, 2C8, 2C9, 3A4, 3A5) wasrecorded (half-life>240 minutes and intrinsic clearance<29 μL/min/nmol)indicating no significant effect on SPL026 and deuterated SPL028analogue metabolism.

TABLE 12 In vitro intrinsic clearance of SPL026 and 2 × D₂-deuteratedSPL028 deuterated compounds and markers through CYP phenotyping using 8human CYPs (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4 andCYP3A5) in E. coli CYPEX membranes. CYP isoform and intrinsic clearance(μL/min/nmol CYP) Cpd 1A2 2B6 2C8 2C9 2C19 2D6 3A4 3A5 DMT (SPL026) <29<29 <29 <29 37 801 <29 <29 DMT in SPL028i <29 <29 <29 <29 40 687 <29 <29DMT in SPL028ii <29 <29 <29 <29 43 803 <29 <29 SPL028i <29 <29 <29 <2939 793 <29 <29 SPL028i in DMT <29 <29 <29 <29 30 914 <29 <29 SPL028i in<29 <29 <29 <29 39 789 <29 <29 SPL028ii SPL028ii <29 <29 <29 <29 39 801<29 <29 SPL028ii in DMT <29 <29 <29 <29 39 806 <29 <29 SPL028ii in <29<29 <29 <29 41 790 <29 <29 SPL028i Carvedilol 231 52 526 4483 142Tacrine 189 Bupropion 51 Ticlopidine 1640 Montelukast 122 Verapamil 1244267 Diclofenac 4731 Propranolol 566 Dextromethorphan 2686 Midazolam 1369623

TABLE 13 In vitro half-life of SPL026 and 2 × D₂-deuterated SPL028deuterated compounds and markers through CYP phenotyping using 8 humanCYPs (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4 andCYP3A5) in E. coli CYPEX membranes. CYP isoform and half-life (min) Cpd1A2 2B6 2C8 2C9 2C19 2D6 3A4 3A5 DMT (SPL026) >240 >240 >240 >240 1899 >240 >240 DMT in SPL028i >240 >240 >240 >240 176 10 >240 >240 DMT inSPL028ii >240 >240 >240 >240 162 9 >240 >240 SPL028i >240 >240 >240 >240180 9 >240 >240 SPL028i in DMT >240 >240 >240 >240 237 8 >240 >240SPL028i in >240 >240 >240 >240 179 9 >240 >240 SPL028iiSPL028ii >240 >240 >240 >240 176 9 >240 >240 SPL028ii inDMT >240 >240 >240 >240 177 9 >240 >240 SPL028ii in >240 >240 >240 >240172 9 >240 >240 SPL028i Carvedilol 30 134 13 2 49 Tacrine 37 Bupropion135 Ticlopidine 4 Montelukast 62 Verapamil 6 26 Diclofenac 1 Propranolol12 Dextromethorphan 3 Midazolam 5 11

TABLE 14 Projected scaled intrinsic clearance of CYP2C19 and CYP2D6isoforms for SPL206, SPL028i and SPL028ii. Projected scaled intrinsicclearance for other CYP isoforms were not calculated as no turnover wasdetected (<29 μl/min/nmol) in phenotyping assay. CYP isoform andprojected scaled intrinsic clearance (μl/min/mg microsomal protein)Compound 2C19 2D6 DMT (SPL026) 0.3 9.5 DMT in SPL028i 0.4 8.1 DMT inSPL028ii 0.4 9.5 SPL028i 0.3 9.4 SPL028i in DMT 0.3 10.8 SPL028i inSPL028ii 0.4 9.3 SPL028ii 0.4 9.5 SPL028ii in DMT 0.4 9.5 SPL028ii inSPL028i 0.4 9.3

Results suggest a role of CYP2D6 and 2C19 in the metabolism of SPL026and D₂-deuterated SPL028 analogues.

CONCLUSION

α-Carbon Deuteration of DMT Increases Metabolic Stability

This series of in vitro investigations on the metabolic stability ofSPL026 and eight different deuterated analogue blends indicate thatdeuteration of the α-carbon increases the metabolic stability of DMT ina progressive manner.

We found different DKIE effects of SPL028 compounds in different humanand animal tissues. The largest DKIE, measured via reduced intrinsicclearance and increased half-life, were recorded in human livermitochondrial fractions. In this fraction the most α-deuterated SPL028compounds, (96.6% D₂) SPL028i and (D₈) SPL028viii saw the largestdifference in metabolic stability relative to un-deuterated SPL026, eachresult saw a ˜10.8 and ˜14.8-fold change from SPL026 respectively.

MAO-A Metabolism is the Predominant Metabolic Pathway of DMT in HumanMitochondrial Fraction

Mitochondrial fractions contain a high proportion of MAO enzymescompared to human liver hepatocytes. This was confirmed by thedifferences in clearance and half-life values of serotonin (MAO-Asubstrate) and benzylamine (MAO-B substrate) positive controls betweenhuman hepatocytes and human liver mitochondrial fraction. Compared tohepatocyte fraction, human liver mitochondria saw a ˜3.9 fold and˜3.6-fold increase in intrinsic clearance for MAO-A substrate and MAO-Bsubstrate respectively. Inclusion of MAO-A inhibitors were shown to havea significant effect on the clearance of SPL026, whereas MAO-Binhibitors caused no change to the metabolic stability of SPL026 inmitochondrial fraction. These findings suggest that α-deuteration of DMTinhibits the oxidative deamination metabolic pathway involving MAO-Aenzymes.

CYP2D6 and CYP2C19 Provide an Alternative Metabolic Pathway for DMT andα-Deuterated-DMT

CYP phenotyping demonstrated a role of CYP2D6 and CYP2C19 enzymemetabolism of SPL026 and 2 different D₂-deuterated (SPL028i, SPL028ii)at equivalent levels. This data indicates that in addition to MAO-A,alternative enzymes are responsible for the metabolism of SPL026 anddeuterated SPL028 compounds.

The invention claimed is:
 1. A method of synthesising a compound offormula (I′):

or a pharmaceutically acceptable salt thereof, comprising reacting acompound of formula (II):

with LiAlH₄ and/or LiAlD₄, wherein the compound of formula (II) is madeby: reacting a compound of formula (III)

with two or more coupling agents to produce an activated compound; and(ii) reacting the activated compound with an amine having the formulaR²R³NH or R²R³ND, wherein: R^(1′) is independently selected from —R⁴,—OPR, —OR⁴, —F, —Cl, —Br and —I; PR is a protecting group, n is selectedfrom 0, 1, 2, 3 or 4; R² is C(^(x)H)₃; R³ is C(^(x)H)₃ or H; each R⁴ isindependently selected from C₁-C₄alkyl; and each ^(x)H and ^(y)H isindependently protium or deuterium, wherein a ratio of deuterium:protiumin a C(^(x)H)₃ moiety in the compound of formula (I′) is greater thanthat found naturally in hydrogen, or a pharmaceutically acceptable saltthereof.
 2. The method of claim 1 wherein a ratio of LiAlH₄ and/orLiAlD₄:compound of formula (II) of 0.8:1 to 1:1 is used.
 3. The methodof claim 1 wherein the two or more coupling agents comprise an additivecoupling agent.
 4. The method of claim 3, wherein the two or morecoupling agents comprise a carbodiimide.
 5. The method of claim 3,wherein the additive coupling agent is selected from the groupconsisting of 1-hydroxybenzotriazole,hydroxy-3,4-dihydro-4-oxo-1,2,3-benzotriazine, N-hydroxysuccinimide,1-hydroxy-7-aza-1H -benzotriazole, ethyl 2-cyano-2-(hydroximino)acetateand 4-(N,N-Dimethylamino)pyridine.
 6. A method of psychedelic-assistedpsychotherapy for treating a psychiatric or neurological disorder,comprising: administering to a patient in need thereof the compound

or a pharmaceutically acceptable salt thereof.
 7. A method ofpsychedelic-assisted psychotherapy for treating a psychiatric orneurological disorder, comprising: administering to a patient in needthereof a compound of formula:

or a pharmaceutically acceptable salt thereof, wherein the patient inneed thereof is subjected to a psychedelic experience induced byadministration of the compound, or a pharmaceutically acceptable saltthereof.